kernel: add and enable MGLRU for Linux 5.15

Backport a preliminary version of Yu Zhao's multi-generational LRU, for
improved memory management. Refresh the patches while at it.

Signed-off-by: Rui Salvaterra <[email protected]>

target/linux/generic/config-5.15

@@ -3195,6 +3195,9 @@ CONFIG_LOG_CPU_MAX_BUF_SHIFT=12
 # CONFIG_LPC_ICH is not set
 # CONFIG_LPC_SCH is not set
 # CONFIG_LP_CONSOLE is not set
+CONFIG_LRU_GEN=y
+CONFIG_LRU_GEN_ENABLED=y
+# CONFIG_LRU_GEN_STATS is not set
 # CONFIG_LSI_ET1011C_PHY is not set
 CONFIG_LSM="lockdown,yama,loadpin,safesetid,integrity"
 CONFIG_LSM_MMAP_MIN_ADDR=65536
@@ -4388,6 +4391,7 @@ CONFIG_NMI_LOG_BUF_SHIFT=13
 # CONFIG_NO_HZ is not set
 # CONFIG_NO_HZ_FULL is not set
 # CONFIG_NO_HZ_IDLE is not set
+CONFIG_NR_LRU_GENS=7
 # CONFIG_NS83820 is not set
 # CONFIG_NTB is not set
 # CONFIG_NTFS3_64BIT_CLUSTER is not set
@@ -6480,6 +6484,7 @@ CONFIG_THIN_ARCHIVES=y
 # CONFIG_THUNDER_NIC_VF is not set
 # CONFIG_TICK_CPU_ACCOUNTING is not set
 CONFIG_TICK_ONESHOT=y
+CONFIG_TIERS_PER_GEN=4
 # CONFIG_TIFM_CORE is not set
 # CONFIG_TIGON3 is not set
 # CONFIG_TIMB_DMA is not set

target/linux/generic/pending-5.15/020-00-mm-x86-arm64-add-arch_has_hw_pte_young.patch

@@ -0,0 +1,169 @@
+From a8e6015d9534f39abc08e6804566af059e498a60 Mon Sep 17 00:00:00 2001
+From: Yu Zhao <[email protected]>
+Date: Wed, 4 Aug 2021 01:31:34 -0600
+Subject: [PATCH 01/10] mm: x86, arm64: add arch_has_hw_pte_young()
+
+Some architectures automatically set the accessed bit in PTEs, e.g.,
+x86 and arm64 v8.2. On architectures that do not have this capability,
+clearing the accessed bit in a PTE triggers a page fault following the
+TLB miss of this PTE.
+
+Being aware of this capability can help make better decisions, i.e.,
+whether to limit the size of each batch of PTEs and the burst of
+batches when clearing the accessed bit.
+
+Signed-off-by: Yu Zhao <[email protected]>
+Change-Id: Ib49b44fb56df3333a2ff1fcc496fb1980b976e7a
+---
+ arch/arm64/include/asm/cpufeature.h |  5 +++++
+ arch/arm64/include/asm/pgtable.h    | 13 ++++++++-----
+ arch/arm64/kernel/cpufeature.c      | 10 ++++++++++
+ arch/arm64/tools/cpucaps            |  1 +
+ arch/x86/include/asm/pgtable.h      |  6 +++---
+ include/linux/pgtable.h             | 13 +++++++++++++
+ mm/memory.c                         | 14 +-------------
+ 7 files changed, 41 insertions(+), 21 deletions(-)
+
+--- a/arch/arm64/include/asm/cpufeature.h
++++ b/arch/arm64/include/asm/cpufeature.h
+@@ -808,6 +808,11 @@ static inline bool system_supports_tlb_r
+ 		cpus_have_const_cap(ARM64_HAS_TLB_RANGE);
+ }
+ 
++static inline bool system_has_hw_af(void)
++{
++	return IS_ENABLED(CONFIG_ARM64_HW_AFDBM) && cpus_have_const_cap(ARM64_HW_AF);
++}
++
+ extern int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
+ 
+ static inline u32 id_aa64mmfr0_parange_to_phys_shift(int parange)
+--- a/arch/arm64/include/asm/pgtable.h
++++ b/arch/arm64/include/asm/pgtable.h
+@@ -999,13 +999,16 @@ static inline void update_mmu_cache(stru
+  * page after fork() + CoW for pfn mappings. We don't always have a
+  * hardware-managed access flag on arm64.
+  */
+-static inline bool arch_faults_on_old_pte(void)
++static inline bool arch_has_hw_pte_young(bool local)
+ {
+-	WARN_ON(preemptible());
++	if (local) {
++		WARN_ON(preemptible());
++		return cpu_has_hw_af();
++	}
+ 
+-	return !cpu_has_hw_af();
++	return system_has_hw_af();
+ }
+-#define arch_faults_on_old_pte		arch_faults_on_old_pte
++#define arch_has_hw_pte_young		arch_has_hw_pte_young
+ 
+ /*
+  * Experimentally, it's cheap to set the access flag in hardware and we
+@@ -1013,7 +1016,7 @@ static inline bool arch_faults_on_old_pt
+  */
+ static inline bool arch_wants_old_prefaulted_pte(void)
+ {
+-	return !arch_faults_on_old_pte();
++	return arch_has_hw_pte_young(true);
+ }
+ #define arch_wants_old_prefaulted_pte	arch_wants_old_prefaulted_pte
+ 
+--- a/arch/arm64/kernel/cpufeature.c
++++ b/arch/arm64/kernel/cpufeature.c
+@@ -2184,6 +2184,16 @@ static const struct arm64_cpu_capabiliti
+ 		.matches = has_hw_dbm,
+ 		.cpu_enable = cpu_enable_hw_dbm,
+ 	},
++	{
++		.desc = "Hardware update of the Access flag",
++		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
++		.capability = ARM64_HW_AF,
++		.sys_reg = SYS_ID_AA64MMFR1_EL1,
++		.sign = FTR_UNSIGNED,
++		.field_pos = ID_AA64MMFR1_HADBS_SHIFT,
++		.min_field_value = 1,
++		.matches = has_cpuid_feature,
++	},
+ #endif
+ 	{
+ 		.desc = "CRC32 instructions",
+--- a/arch/arm64/tools/cpucaps
++++ b/arch/arm64/tools/cpucaps
+@@ -35,6 +35,7 @@ HAS_STAGE2_FWB
+ HAS_SYSREG_GIC_CPUIF
+ HAS_TLB_RANGE
+ HAS_VIRT_HOST_EXTN
++HW_AF
+ HW_DBM
+ KVM_PROTECTED_MODE
+ MISMATCHED_CACHE_TYPE
+--- a/arch/x86/include/asm/pgtable.h
++++ b/arch/x86/include/asm/pgtable.h
+@@ -1397,10 +1397,10 @@ static inline bool arch_has_pfn_modify_c
+ 	return boot_cpu_has_bug(X86_BUG_L1TF);
+ }
+ 
+-#define arch_faults_on_old_pte arch_faults_on_old_pte
+-static inline bool arch_faults_on_old_pte(void)
++#define arch_has_hw_pte_young arch_has_hw_pte_young
++static inline bool arch_has_hw_pte_young(bool local)
+ {
+-	return false;
++	return true;
+ }
+ 
+ #endif	/* __ASSEMBLY__ */
+--- a/include/linux/pgtable.h
++++ b/include/linux/pgtable.h
+@@ -259,6 +259,19 @@ static inline int pmdp_clear_flush_young
+ #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+ #endif
+ 
++#ifndef arch_has_hw_pte_young
++/*
++ * Return whether the accessed bit is supported by the local CPU or all CPUs.
++ *
++ * Those arches which have hw access flag feature need to implement their own
++ * helper. By default, "false" means pagefault will be hit on old pte.
++ */
++static inline bool arch_has_hw_pte_young(bool local)
++{
++	return false;
++}
++#endif
++
+ #ifndef __HAVE_ARCH_PTEP_GET_AND_CLEAR
+ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
+ 				       unsigned long address,
+--- a/mm/memory.c
++++ b/mm/memory.c
+@@ -121,18 +121,6 @@ int randomize_va_space __read_mostly =
+ 					2;
+ #endif
+ 
+-#ifndef arch_faults_on_old_pte
+-static inline bool arch_faults_on_old_pte(void)
+-{
+-	/*
+-	 * Those arches which don't have hw access flag feature need to
+-	 * implement their own helper. By default, "true" means pagefault
+-	 * will be hit on old pte.
+-	 */
+-	return true;
+-}
+-#endif
+-
+ #ifndef arch_wants_old_prefaulted_pte
+ static inline bool arch_wants_old_prefaulted_pte(void)
+ {
+@@ -2782,7 +2770,7 @@ static inline bool cow_user_page(struct
+ 	 * On architectures with software "accessed" bits, we would
+ 	 * take a double page fault, so mark it accessed here.
+ 	 */
+-	if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
++	if (!arch_has_hw_pte_young(true) && !pte_young(vmf->orig_pte)) {
+ 		pte_t entry;
+ 
+ 		vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);

target/linux/generic/pending-5.15/020-01-mm-x86-add-CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG.patch

@@ -0,0 +1,111 @@
+From f8b663bbfa30af5515e222fd74df20ea4e8393a2 Mon Sep 17 00:00:00 2001
+From: Yu Zhao <[email protected]>
+Date: Sat, 26 Sep 2020 21:17:18 -0600
+Subject: [PATCH 02/10] mm: x86: add CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG
+
+Some architectures support the accessed bit on non-leaf PMD entries,
+e.g., x86_64 sets the accessed bit on a non-leaf PMD entry when using
+it as part of linear address translation [1]. As an optimization, page
+table walkers who are interested in the accessed bit can skip the PTEs
+under a non-leaf PMD entry if the accessed bit is cleared on this PMD
+entry.
+
+Although an inline function may be preferable, this capability is
+added as a configuration option to look consistent when used with the
+existing macros.
+
+[1]: Intel 64 and IA-32 Architectures Software Developer's Manual
+     Volume 3 (June 2021), section 4.8
+
+Signed-off-by: Yu Zhao <[email protected]>
+Tested-by: Konstantin Kharlamov <[email protected]>
+Change-Id: I1a17be3ae926f721f7b17ea1539e5c39e8c4f9a8
+---
+ arch/Kconfig                   | 9 +++++++++
+ arch/x86/Kconfig               | 1 +
+ arch/x86/include/asm/pgtable.h | 3 ++-
+ arch/x86/mm/pgtable.c          | 5 ++++-
+ include/linux/pgtable.h        | 4 ++--
+ 5 files changed, 18 insertions(+), 4 deletions(-)
+
+--- a/arch/Kconfig
++++ b/arch/Kconfig
+@@ -1295,6 +1295,15 @@ config ARCH_HAS_ELFCORE_COMPAT
+ config ARCH_HAS_PARANOID_L1D_FLUSH
+ 	bool
+ 
++config ARCH_HAS_NONLEAF_PMD_YOUNG
++	bool
++	depends on PGTABLE_LEVELS > 2
++	help
++	  Architectures that select this are able to set the accessed bit on
++	  non-leaf PMD entries in addition to leaf PTE entries where pages are
++	  mapped. For them, page table walkers that clear the accessed bit may
++	  stop at non-leaf PMD entries if they do not see the accessed bit.
++
+ source "kernel/gcov/Kconfig"
+ 
+ source "scripts/gcc-plugins/Kconfig"
+--- a/arch/x86/Kconfig
++++ b/arch/x86/Kconfig
+@@ -84,6 +84,7 @@ config X86
+ 	select ARCH_HAS_PMEM_API		if X86_64
+ 	select ARCH_HAS_PTE_DEVMAP		if X86_64
+ 	select ARCH_HAS_PTE_SPECIAL
++	select ARCH_HAS_NONLEAF_PMD_YOUNG	if X86_64
+ 	select ARCH_HAS_UACCESS_FLUSHCACHE	if X86_64
+ 	select ARCH_HAS_COPY_MC			if X86_64
+ 	select ARCH_HAS_SET_MEMORY
+--- a/arch/x86/include/asm/pgtable.h
++++ b/arch/x86/include/asm/pgtable.h
+@@ -817,7 +817,8 @@ static inline unsigned long pmd_page_vad
+ 
+ static inline int pmd_bad(pmd_t pmd)
+ {
+-	return (pmd_flags(pmd) & ~_PAGE_USER) != _KERNPG_TABLE;
++	return (pmd_flags(pmd) & ~(_PAGE_USER | _PAGE_ACCESSED)) !=
++	       (_KERNPG_TABLE & ~_PAGE_ACCESSED);
+ }
+ 
+ static inline unsigned long pages_to_mb(unsigned long npg)
+--- a/arch/x86/mm/pgtable.c
++++ b/arch/x86/mm/pgtable.c
+@@ -550,7 +550,7 @@ int ptep_test_and_clear_young(struct vm_
+ 	return ret;
+ }
+ 
+-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
++#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG)
+ int pmdp_test_and_clear_young(struct vm_area_struct *vma,
+ 			      unsigned long addr, pmd_t *pmdp)
+ {
+@@ -562,6 +562,9 @@ int pmdp_test_and_clear_young(struct vm_
+ 
+ 	return ret;
+ }
++#endif
++
++#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ int pudp_test_and_clear_young(struct vm_area_struct *vma,
+ 			      unsigned long addr, pud_t *pudp)
+ {
+--- a/include/linux/pgtable.h
++++ b/include/linux/pgtable.h
+@@ -212,7 +212,7 @@ static inline int ptep_test_and_clear_yo
+ #endif
+ 
+ #ifndef __HAVE_ARCH_PMDP_TEST_AND_CLEAR_YOUNG
+-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
++#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG)
+ static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma,
+ 					    unsigned long address,
+ 					    pmd_t *pmdp)
+@@ -233,7 +233,7 @@ static inline int pmdp_test_and_clear_yo
+ 	BUILD_BUG();
+ 	return 0;
+ }
+-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
++#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG */
+ #endif
+ 
+ #ifndef __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH

target/linux/generic/pending-5.15/020-02-mm-vmscan.c-refactor-shrink_node.patch

@@ -0,0 +1,224 @@
+From a810f8e2f1bdd0707eaf05c8b4ba84a3ff2801bd Mon Sep 17 00:00:00 2001
+From: Yu Zhao <[email protected]>
+Date: Sun, 27 Sep 2020 20:49:08 -0600
+Subject: [PATCH 03/10] mm/vmscan.c: refactor shrink_node()
+
+This patch refactors shrink_node(). This will make the upcoming
+changes to mm/vmscan.c more readable.
+
+Signed-off-by: Yu Zhao <[email protected]>
+Tested-by: Konstantin Kharlamov <[email protected]>
+Change-Id: Iae734b5b4030205b7db6e8c841f747b6f6ae1a04
+---
+ mm/vmscan.c | 186 +++++++++++++++++++++++++++-------------------------
+ 1 file changed, 98 insertions(+), 88 deletions(-)
+
+--- a/mm/vmscan.c
++++ b/mm/vmscan.c
+@@ -2562,6 +2562,103 @@ enum scan_balance {
+ 	SCAN_FILE,
+ };
+ 
++static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc)
++{
++	unsigned long file;
++	struct lruvec *target_lruvec;
++
++	target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);
++
++	/*
++	 * Determine the scan balance between anon and file LRUs.
++	 */
++	spin_lock_irq(&target_lruvec->lru_lock);
++	sc->anon_cost = target_lruvec->anon_cost;
++	sc->file_cost = target_lruvec->file_cost;
++	spin_unlock_irq(&target_lruvec->lru_lock);
++
++	/*
++	 * Target desirable inactive:active list ratios for the anon
++	 * and file LRU lists.
++	 */
++	if (!sc->force_deactivate) {
++		unsigned long refaults;
++
++		refaults = lruvec_page_state(target_lruvec,
++				WORKINGSET_ACTIVATE_ANON);
++		if (refaults != target_lruvec->refaults[0] ||
++			inactive_is_low(target_lruvec, LRU_INACTIVE_ANON))
++			sc->may_deactivate |= DEACTIVATE_ANON;
++		else
++			sc->may_deactivate &= ~DEACTIVATE_ANON;
++
++		/*
++		 * When refaults are being observed, it means a new
++		 * workingset is being established. Deactivate to get
++		 * rid of any stale active pages quickly.
++		 */
++		refaults = lruvec_page_state(target_lruvec,
++				WORKINGSET_ACTIVATE_FILE);
++		if (refaults != target_lruvec->refaults[1] ||
++		    inactive_is_low(target_lruvec, LRU_INACTIVE_FILE))
++			sc->may_deactivate |= DEACTIVATE_FILE;
++		else
++			sc->may_deactivate &= ~DEACTIVATE_FILE;
++	} else
++		sc->may_deactivate = DEACTIVATE_ANON | DEACTIVATE_FILE;
++
++	/*
++	 * If we have plenty of inactive file pages that aren't
++	 * thrashing, try to reclaim those first before touching
++	 * anonymous pages.
++	 */
++	file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE);
++	if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE))
++		sc->cache_trim_mode = 1;
++	else
++		sc->cache_trim_mode = 0;
++
++	/*
++	 * Prevent the reclaimer from falling into the cache trap: as
++	 * cache pages start out inactive, every cache fault will tip
++	 * the scan balance towards the file LRU.  And as the file LRU
++	 * shrinks, so does the window for rotation from references.
++	 * This means we have a runaway feedback loop where a tiny
++	 * thrashing file LRU becomes infinitely more attractive than
++	 * anon pages.  Try to detect this based on file LRU size.
++	 */
++	if (!cgroup_reclaim(sc)) {
++		unsigned long total_high_wmark = 0;
++		unsigned long free, anon;
++		int z;
++
++		free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
++		file = node_page_state(pgdat, NR_ACTIVE_FILE) +
++			   node_page_state(pgdat, NR_INACTIVE_FILE);
++
++		for (z = 0; z < MAX_NR_ZONES; z++) {
++			struct zone *zone = &pgdat->node_zones[z];
++
++			if (!managed_zone(zone))
++				continue;
++
++			total_high_wmark += high_wmark_pages(zone);
++		}
++
++		/*
++		 * Consider anon: if that's low too, this isn't a
++		 * runaway file reclaim problem, but rather just
++		 * extreme pressure. Reclaim as per usual then.
++		 */
++		anon = node_page_state(pgdat, NR_INACTIVE_ANON);
++
++		sc->file_is_tiny =
++			file + free <= total_high_wmark &&
++			!(sc->may_deactivate & DEACTIVATE_ANON) &&
++			anon >> sc->priority;
++	}
++}
++
+ /*
+  * Determine how aggressively the anon and file LRU lists should be
+  * scanned.  The relative value of each set of LRU lists is determined
+@@ -3032,7 +3129,6 @@ static void shrink_node(pg_data_t *pgdat
+ 	unsigned long nr_reclaimed, nr_scanned;
+ 	struct lruvec *target_lruvec;
+ 	bool reclaimable = false;
+-	unsigned long file;
+ 
+ 	target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);
+ 
+@@ -3048,93 +3144,7 @@ again:
+ 	nr_reclaimed = sc->nr_reclaimed;
+ 	nr_scanned = sc->nr_scanned;
+ 
+-	/*
+-	 * Determine the scan balance between anon and file LRUs.
+-	 */
+-	spin_lock_irq(&target_lruvec->lru_lock);
+-	sc->anon_cost = target_lruvec->anon_cost;
+-	sc->file_cost = target_lruvec->file_cost;
+-	spin_unlock_irq(&target_lruvec->lru_lock);
+-
+-	/*
+-	 * Target desirable inactive:active list ratios for the anon
+-	 * and file LRU lists.
+-	 */
+-	if (!sc->force_deactivate) {
+-		unsigned long refaults;
+-
+-		refaults = lruvec_page_state(target_lruvec,
+-				WORKINGSET_ACTIVATE_ANON);
+-		if (refaults != target_lruvec->refaults[0] ||
+-			inactive_is_low(target_lruvec, LRU_INACTIVE_ANON))
+-			sc->may_deactivate |= DEACTIVATE_ANON;
+-		else
+-			sc->may_deactivate &= ~DEACTIVATE_ANON;
+-
+-		/*
+-		 * When refaults are being observed, it means a new
+-		 * workingset is being established. Deactivate to get
+-		 * rid of any stale active pages quickly.
+-		 */
+-		refaults = lruvec_page_state(target_lruvec,
+-				WORKINGSET_ACTIVATE_FILE);
+-		if (refaults != target_lruvec->refaults[1] ||
+-		    inactive_is_low(target_lruvec, LRU_INACTIVE_FILE))
+-			sc->may_deactivate |= DEACTIVATE_FILE;
+-		else
+-			sc->may_deactivate &= ~DEACTIVATE_FILE;
+-	} else
+-		sc->may_deactivate = DEACTIVATE_ANON | DEACTIVATE_FILE;
+-
+-	/*
+-	 * If we have plenty of inactive file pages that aren't
+-	 * thrashing, try to reclaim those first before touching
+-	 * anonymous pages.
+-	 */
+-	file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE);
+-	if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE))
+-		sc->cache_trim_mode = 1;
+-	else
+-		sc->cache_trim_mode = 0;
+-
+-	/*
+-	 * Prevent the reclaimer from falling into the cache trap: as
+-	 * cache pages start out inactive, every cache fault will tip
+-	 * the scan balance towards the file LRU.  And as the file LRU
+-	 * shrinks, so does the window for rotation from references.
+-	 * This means we have a runaway feedback loop where a tiny
+-	 * thrashing file LRU becomes infinitely more attractive than
+-	 * anon pages.  Try to detect this based on file LRU size.
+-	 */
+-	if (!cgroup_reclaim(sc)) {
+-		unsigned long total_high_wmark = 0;
+-		unsigned long free, anon;
+-		int z;
+-
+-		free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
+-		file = node_page_state(pgdat, NR_ACTIVE_FILE) +
+-			   node_page_state(pgdat, NR_INACTIVE_FILE);
+-
+-		for (z = 0; z < MAX_NR_ZONES; z++) {
+-			struct zone *zone = &pgdat->node_zones[z];
+-			if (!managed_zone(zone))
+-				continue;
+-
+-			total_high_wmark += high_wmark_pages(zone);
+-		}
+-
+-		/*
+-		 * Consider anon: if that's low too, this isn't a
+-		 * runaway file reclaim problem, but rather just
+-		 * extreme pressure. Reclaim as per usual then.
+-		 */
+-		anon = node_page_state(pgdat, NR_INACTIVE_ANON);
+-
+-		sc->file_is_tiny =
+-			file + free <= total_high_wmark &&
+-			!(sc->may_deactivate & DEACTIVATE_ANON) &&
+-			anon >> sc->priority;
+-	}
++	prepare_scan_count(pgdat, sc);
+ 
+ 	shrink_node_memcgs(pgdat, sc);
+ 

target/linux/generic/pending-5.15/020-03-mm-multigenerational-lru-groundwork.patch

@@ -0,0 +1,996 @@
+From 05f366c941ae2bb8ba21c79fafcb747a5a6b967b Mon Sep 17 00:00:00 2001
+From: Yu Zhao <[email protected]>
+Date: Mon, 25 Jan 2021 21:12:33 -0700
+Subject: [PATCH 04/10] mm: multigenerational lru: groundwork
+
+For each lruvec, evictable pages are divided into multiple
+generations. The youngest generation number is stored in
+lrugen->max_seq for both anon and file types as they are aged on an
+equal footing. The oldest generation numbers are stored in
+lrugen->min_seq[] separately for anon and file types as clean file
+pages can be evicted regardless of swap constraints. These three
+variables are monotonically increasing. Generation numbers are
+truncated into order_base_2(MAX_NR_GENS+1) bits in order to fit into
+page->flags. The sliding window technique is used to prevent truncated
+generation numbers from overlapping. Each truncated generation number
+is an index to
+lrugen->lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES].
+
+The framework comprises two conceptually independent components: the
+aging, which produces young generations, and the eviction, which
+consumes old generations. Both can be invoked independently from user
+space for the purpose of working set estimation and proactive reclaim.
+
+The protection of hot pages and the selection of cold pages are based
+on page access types and patterns. There are two access types: one via
+page tables and the other via file descriptors. The protection of the
+former type is by design stronger because:
+  1) The uncertainty in determining the access patterns of the former
+  type is higher due to the coalesced nature of the accessed bit.
+  2) The cost of evicting the former type is higher due to the TLB
+  flushes required and the likelihood of involving I/O.
+  3) The penalty of under-protecting the former type is higher because
+  applications usually do not prepare themselves for major faults like
+  they do for blocked I/O. For example, client applications commonly
+  dedicate blocked I/O to separate threads to avoid UI janks that
+  negatively affect user experience.
+
+There are also two access patterns: one with temporal locality and the
+other without. The latter pattern, e.g., random and sequential, needs
+to be explicitly excluded to avoid weakening the protection of the
+former pattern. Generally the former type follows the former pattern
+unless MADV_SEQUENTIAL is specified and the latter type follows the
+latter pattern unless outlying refaults have been observed.
+
+Upon faulting, a page is added to the youngest generation, which
+provides the strongest protection as the eviction will not consider
+this page before the aging has scanned it at least twice. The first
+scan clears the accessed bit set during the initial fault. And the
+second scan makes sure this page has not been used since the first
+scan. A page from any other generations is brought back to the
+youngest generation whenever the aging finds the accessed bit set on
+any of the PTEs mapping this page.
+
+Unmapped pages are initially added to the oldest generation and then
+conditionally protected by tiers. This is done later [PATCH 07/10].
+
+Signed-off-by: Yu Zhao <[email protected]>
+Tested-by: Konstantin Kharlamov <[email protected]>
+Change-Id: I71de7cd15b8dfa6f9fdd838023474693c4fee0a7
+---
+ fs/fuse/dev.c                     |   3 +-
+ include/linux/cgroup.h            |  15 +-
+ include/linux/mm.h                |  36 ++++
+ include/linux/mm_inline.h         | 182 ++++++++++++++++++++
+ include/linux/mmzone.h            |  70 ++++++++
+ include/linux/page-flags-layout.h |  19 ++-
+ include/linux/page-flags.h        |   4 +-
+ include/linux/sched.h             |   3 +
+ kernel/bounds.c                   |   3 +
+ kernel/cgroup/cgroup-internal.h   |   1 -
+ mm/huge_memory.c                  |   3 +-
+ mm/memcontrol.c                   |   1 +
+ mm/memory.c                       |   7 +
+ mm/mm_init.c                      |   6 +-
+ mm/page_alloc.c                   |   1 +
+ mm/swap.c                         |   9 +-
+ mm/swapfile.c                     |   2 +
+ mm/vmscan.c                       | 268 ++++++++++++++++++++++++++++++
+ 18 files changed, 618 insertions(+), 15 deletions(-)
+
+--- a/fs/fuse/dev.c
++++ b/fs/fuse/dev.c
+@@ -785,7 +785,8 @@ static int fuse_check_page(struct page *
+ 	       1 << PG_active |
+ 	       1 << PG_workingset |
+ 	       1 << PG_reclaim |
+-	       1 << PG_waiters))) {
++	       1 << PG_waiters |
++	       LRU_GEN_MASK | LRU_REFS_MASK))) {
+ 		dump_page(page, "fuse: trying to steal weird page");
+ 		return 1;
+ 	}
+--- a/include/linux/cgroup.h
++++ b/include/linux/cgroup.h
+@@ -432,6 +432,18 @@ static inline void cgroup_put(struct cgr
+ 	css_put(&cgrp->self);
+ }
+ 
++extern struct mutex cgroup_mutex;
++
++static inline void cgroup_lock(void)
++{
++	mutex_lock(&cgroup_mutex);
++}
++
++static inline void cgroup_unlock(void)
++{
++	mutex_unlock(&cgroup_mutex);
++}
++
+ /**
+  * task_css_set_check - obtain a task's css_set with extra access conditions
+  * @task: the task to obtain css_set for
+@@ -446,7 +458,6 @@ static inline void cgroup_put(struct cgr
+  * as locks used during the cgroup_subsys::attach() methods.
+  */
+ #ifdef CONFIG_PROVE_RCU
+-extern struct mutex cgroup_mutex;
+ extern spinlock_t css_set_lock;
+ #define task_css_set_check(task, __c)					\
+ 	rcu_dereference_check((task)->cgroups,				\
+@@ -707,6 +718,8 @@ struct cgroup;
+ static inline u64 cgroup_id(const struct cgroup *cgrp) { return 1; }
+ static inline void css_get(struct cgroup_subsys_state *css) {}
+ static inline void css_put(struct cgroup_subsys_state *css) {}
++static inline void cgroup_lock(void) {}
++static inline void cgroup_unlock(void) {}
+ static inline int cgroup_attach_task_all(struct task_struct *from,
+ 					 struct task_struct *t) { return 0; }
+ static inline int cgroupstats_build(struct cgroupstats *stats,
+--- a/include/linux/mm.h
++++ b/include/linux/mm.h
+@@ -1093,6 +1093,8 @@ vm_fault_t finish_mkwrite_fault(struct v
+ #define ZONES_PGOFF		(NODES_PGOFF - ZONES_WIDTH)
+ #define LAST_CPUPID_PGOFF	(ZONES_PGOFF - LAST_CPUPID_WIDTH)
+ #define KASAN_TAG_PGOFF		(LAST_CPUPID_PGOFF - KASAN_TAG_WIDTH)
++#define LRU_GEN_PGOFF		(KASAN_TAG_PGOFF - LRU_GEN_WIDTH)
++#define LRU_REFS_PGOFF		(LRU_GEN_PGOFF - LRU_REFS_WIDTH)
+ 
+ /*
+  * Define the bit shifts to access each section.  For non-existent
+@@ -1807,6 +1809,40 @@ static inline void unmap_mapping_range(s
+ 		loff_t const holebegin, loff_t const holelen, int even_cows) { }
+ #endif
+ 
++#ifdef CONFIG_LRU_GEN
++static inline void task_enter_nonseq_fault(void)
++{
++	WARN_ON(current->in_nonseq_fault);
++
++	current->in_nonseq_fault = 1;
++}
++
++static inline void task_exit_nonseq_fault(void)
++{
++	WARN_ON(!current->in_nonseq_fault);
++
++	current->in_nonseq_fault = 0;
++}
++
++static inline bool task_in_nonseq_fault(void)
++{
++	return current->in_nonseq_fault;
++}
++#else
++static inline void task_enter_nonseq_fault(void)
++{
++}
++
++static inline void task_exit_nonseq_fault(void)
++{
++}
++
++static inline bool task_in_nonseq_fault(void)
++{
++	return false;
++}
++#endif /* CONFIG_LRU_GEN */
++
+ static inline void unmap_shared_mapping_range(struct address_space *mapping,
+ 		loff_t const holebegin, loff_t const holelen)
+ {
+--- a/include/linux/mm_inline.h
++++ b/include/linux/mm_inline.h
+@@ -79,11 +79,187 @@ static __always_inline enum lru_list pag
+ 	return lru;
+ }
+ 
++#ifdef CONFIG_LRU_GEN
++
++static inline bool lru_gen_enabled(void)
++{
++#ifdef CONFIG_LRU_GEN_ENABLED
++	DECLARE_STATIC_KEY_TRUE(lru_gen_static_key);
++
++	return static_branch_likely(&lru_gen_static_key);
++#else
++	DECLARE_STATIC_KEY_FALSE(lru_gen_static_key);
++
++	return static_branch_unlikely(&lru_gen_static_key);
++#endif
++}
++
++/* Return an index within the sliding window that tracks MAX_NR_GENS generations. */
++static inline int lru_gen_from_seq(unsigned long seq)
++{
++	return seq % MAX_NR_GENS;
++}
++
++/* The youngest and the second youngest generations are counted as active. */
++static inline bool lru_gen_is_active(struct lruvec *lruvec, int gen)
++{
++	unsigned long max_seq = lruvec->evictable.max_seq;
++
++	VM_BUG_ON(gen >= MAX_NR_GENS);
++
++	return gen == lru_gen_from_seq(max_seq) || gen == lru_gen_from_seq(max_seq - 1);
++}
++
++/* Update the sizes of the multigenerational lru lists. */
++static inline void lru_gen_update_size(struct page *page, struct lruvec *lruvec,
++				       int old_gen, int new_gen)
++{
++	int type = page_is_file_lru(page);
++	int zone = page_zonenum(page);
++	int delta = thp_nr_pages(page);
++	enum lru_list lru = type * LRU_FILE;
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	lockdep_assert_held(&lruvec->lru_lock);
++	VM_BUG_ON(old_gen != -1 && old_gen >= MAX_NR_GENS);
++	VM_BUG_ON(new_gen != -1 && new_gen >= MAX_NR_GENS);
++	VM_BUG_ON(old_gen == -1 && new_gen == -1);
++
++	if (old_gen >= 0)
++		WRITE_ONCE(lrugen->sizes[old_gen][type][zone],
++			   lrugen->sizes[old_gen][type][zone] - delta);
++	if (new_gen >= 0)
++		WRITE_ONCE(lrugen->sizes[new_gen][type][zone],
++			   lrugen->sizes[new_gen][type][zone] + delta);
++
++	if (old_gen < 0) {
++		if (lru_gen_is_active(lruvec, new_gen))
++			lru += LRU_ACTIVE;
++		update_lru_size(lruvec, lru, zone, delta);
++		return;
++	}
++
++	if (new_gen < 0) {
++		if (lru_gen_is_active(lruvec, old_gen))
++			lru += LRU_ACTIVE;
++		update_lru_size(lruvec, lru, zone, -delta);
++		return;
++	}
++
++	if (!lru_gen_is_active(lruvec, old_gen) && lru_gen_is_active(lruvec, new_gen)) {
++		update_lru_size(lruvec, lru, zone, -delta);
++		update_lru_size(lruvec, lru + LRU_ACTIVE, zone, delta);
++	}
++
++	VM_BUG_ON(lru_gen_is_active(lruvec, old_gen) && !lru_gen_is_active(lruvec, new_gen));
++}
++
++/* Add a page to one of the multigenerational lru lists. Return true on success. */
++static inline bool lru_gen_add_page(struct page *page, struct lruvec *lruvec, bool reclaiming)
++{
++	int gen;
++	unsigned long old_flags, new_flags;
++	int type = page_is_file_lru(page);
++	int zone = page_zonenum(page);
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	if (PageUnevictable(page) || !lrugen->enabled[type])
++		return false;
++	/*
++	 * If a page shouldn't be considered for eviction, i.e., a page mapped
++	 * upon fault during which the accessed bit is set, add it to the
++	 * youngest generation.
++	 *
++	 * If a page can't be evicted immediately, i.e., an anon page not in
++	 * swap cache or a dirty page pending writeback, add it to the second
++	 * oldest generation.
++	 *
++	 * If a page could be evicted immediately, e.g., a clean page, add it to
++	 * the oldest generation.
++	 */
++	if (PageActive(page))
++		gen = lru_gen_from_seq(lrugen->max_seq);
++	else if ((!type && !PageSwapCache(page)) ||
++		 (PageReclaim(page) && (PageDirty(page) || PageWriteback(page))))
++		gen = lru_gen_from_seq(lrugen->min_seq[type] + 1);
++	else
++		gen = lru_gen_from_seq(lrugen->min_seq[type]);
++
++	do {
++		new_flags = old_flags = READ_ONCE(page->flags);
++		VM_BUG_ON_PAGE(new_flags & LRU_GEN_MASK, page);
++
++		new_flags &= ~(LRU_GEN_MASK | BIT(PG_active));
++		new_flags |= (gen + 1UL) << LRU_GEN_PGOFF;
++	} while (cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
++
++	lru_gen_update_size(page, lruvec, -1, gen);
++	/* for rotate_reclaimable_page() */
++	if (reclaiming)
++		list_add_tail(&page->lru, &lrugen->lists[gen][type][zone]);
++	else
++		list_add(&page->lru, &lrugen->lists[gen][type][zone]);
++
++	return true;
++}
++
++/* Delete a page from one of the multigenerational lru lists. Return true on success. */
++static inline bool lru_gen_del_page(struct page *page, struct lruvec *lruvec, bool reclaiming)
++{
++	int gen;
++	unsigned long old_flags, new_flags;
++
++	do {
++		new_flags = old_flags = READ_ONCE(page->flags);
++		if (!(new_flags & LRU_GEN_MASK))
++			return false;
++
++		VM_BUG_ON_PAGE(PageActive(page), page);
++		VM_BUG_ON_PAGE(PageUnevictable(page), page);
++
++		gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
++
++		new_flags &= ~LRU_GEN_MASK;
++		/* for shrink_page_list() */
++		if (reclaiming)
++			new_flags &= ~(BIT(PG_referenced) | BIT(PG_reclaim));
++		else if (lru_gen_is_active(lruvec, gen))
++			new_flags |= BIT(PG_active);
++	} while (cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
++
++	lru_gen_update_size(page, lruvec, gen, -1);
++	list_del(&page->lru);
++
++	return true;
++}
++
++#else
++
++static inline bool lru_gen_enabled(void)
++{
++	return false;
++}
++
++static inline bool lru_gen_add_page(struct page *page, struct lruvec *lruvec, bool reclaiming)
++{
++	return false;
++}
++
++static inline bool lru_gen_del_page(struct page *page, struct lruvec *lruvec, bool reclaiming)
++{
++	return false;
++}
++
++#endif /* CONFIG_LRU_GEN */
++
+ static __always_inline void add_page_to_lru_list(struct page *page,
+ 				struct lruvec *lruvec)
+ {
+ 	enum lru_list lru = page_lru(page);
+ 
++	if (lru_gen_add_page(page, lruvec, false))
++		return;
++
+ 	update_lru_size(lruvec, lru, page_zonenum(page), thp_nr_pages(page));
+ 	list_add(&page->lru, &lruvec->lists[lru]);
+ }
+@@ -93,6 +269,9 @@ static __always_inline void add_page_to_
+ {
+ 	enum lru_list lru = page_lru(page);
+ 
++	if (lru_gen_add_page(page, lruvec, true))
++		return;
++
+ 	update_lru_size(lruvec, lru, page_zonenum(page), thp_nr_pages(page));
+ 	list_add_tail(&page->lru, &lruvec->lists[lru]);
+ }
+@@ -100,6 +279,9 @@ static __always_inline void add_page_to_
+ static __always_inline void del_page_from_lru_list(struct page *page,
+ 				struct lruvec *lruvec)
+ {
++	if (lru_gen_del_page(page, lruvec, false))
++		return;
++
+ 	list_del(&page->lru);
+ 	update_lru_size(lruvec, page_lru(page), page_zonenum(page),
+ 			-thp_nr_pages(page));
+--- a/include/linux/mmzone.h
++++ b/include/linux/mmzone.h
+@@ -294,6 +294,72 @@ enum lruvec_flags {
+ 					 */
+ };
+ 
++struct lruvec;
++
++#define LRU_GEN_MASK		((BIT(LRU_GEN_WIDTH) - 1) << LRU_GEN_PGOFF)
++#define LRU_REFS_MASK		((BIT(LRU_REFS_WIDTH) - 1) << LRU_REFS_PGOFF)
++
++#ifdef CONFIG_LRU_GEN
++
++/*
++ * For each lruvec, evictable pages are divided into multiple generations. The
++ * youngest and the oldest generation numbers, AKA max_seq and min_seq, are
++ * monotonically increasing. The sliding window technique is used to track at
++ * least MIN_NR_GENS and at most MAX_NR_GENS generations. An offset within the
++ * window, AKA gen, indexes an array of per-type and per-zone lists for the
++ * corresponding generation. The counter in page->flags stores gen+1 while a
++ * page is on one of the multigenerational lru lists. Otherwise, it stores 0.
++ *
++ * After a page is faulted in, the aging must check the accessed bit at least
++ * twice before the eviction would consider it. The first check clears the
++ * accessed bit set during the initial fault. The second check makes sure this
++ * page hasn't been used since then.
++ */
++#define MIN_NR_GENS		2
++#define MAX_NR_GENS		((unsigned int)CONFIG_NR_LRU_GENS)
++
++struct lrugen {
++	/* the aging increments the max generation number */
++	unsigned long max_seq;
++	/* the eviction increments the min generation numbers */
++	unsigned long min_seq[ANON_AND_FILE];
++	/* the birth time of each generation in jiffies */
++	unsigned long timestamps[MAX_NR_GENS];
++	/* the multigenerational lru lists */
++	struct list_head lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
++	/* the sizes of the multigenerational lru lists in pages */
++	unsigned long sizes[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
++	/* whether the multigenerational lru is enabled */
++	bool enabled[ANON_AND_FILE];
++};
++
++#define MAX_BATCH_SIZE		8192
++
++void lru_gen_init_state(struct mem_cgroup *memcg, struct lruvec *lruvec);
++void lru_gen_change_state(bool enable, bool main, bool swap);
++
++#ifdef CONFIG_MEMCG
++void lru_gen_init_memcg(struct mem_cgroup *memcg);
++#endif
++
++#else /* !CONFIG_LRU_GEN */
++
++static inline void lru_gen_init_state(struct mem_cgroup *memcg, struct lruvec *lruvec)
++{
++}
++
++static inline void lru_gen_change_state(bool enable, bool main, bool swap)
++{
++}
++
++#ifdef CONFIG_MEMCG
++static inline void lru_gen_init_memcg(struct mem_cgroup *memcg)
++{
++}
++#endif
++
++#endif /* CONFIG_LRU_GEN */
++
+ struct lruvec {
+ 	struct list_head		lists[NR_LRU_LISTS];
+ 	/* per lruvec lru_lock for memcg */
+@@ -311,6 +377,10 @@ struct lruvec {
+ 	unsigned long			refaults[ANON_AND_FILE];
+ 	/* Various lruvec state flags (enum lruvec_flags) */
+ 	unsigned long			flags;
++#ifdef CONFIG_LRU_GEN
++	/* unevictable pages are on LRU_UNEVICTABLE */
++	struct lrugen			evictable;
++#endif
+ #ifdef CONFIG_MEMCG
+ 	struct pglist_data *pgdat;
+ #endif
+--- a/include/linux/page-flags-layout.h
++++ b/include/linux/page-flags-layout.h
+@@ -26,6 +26,14 @@
+ 
+ #define ZONES_WIDTH		ZONES_SHIFT
+ 
++#ifdef CONFIG_LRU_GEN
++/* LRU_GEN_WIDTH is generated from order_base_2(CONFIG_NR_LRU_GENS + 1). */
++#define LRU_REFS_WIDTH		(CONFIG_TIERS_PER_GEN - 2)
++#else
++#define LRU_GEN_WIDTH		0
++#define LRU_REFS_WIDTH		0
++#endif /* CONFIG_LRU_GEN */
++
+ #ifdef CONFIG_SPARSEMEM
+ #include <asm/sparsemem.h>
+ #define SECTIONS_SHIFT	(MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
+@@ -55,7 +63,8 @@
+ #define SECTIONS_WIDTH		0
+ #endif
+ 
+-#if ZONES_WIDTH + SECTIONS_WIDTH + NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
++#if ZONES_WIDTH + LRU_GEN_WIDTH + LRU_REFS_WIDTH + SECTIONS_WIDTH + NODES_SHIFT \
++	<= BITS_PER_LONG - NR_PAGEFLAGS
+ #define NODES_WIDTH		NODES_SHIFT
+ #elif defined(CONFIG_SPARSEMEM_VMEMMAP)
+ #error "Vmemmap: No space for nodes field in page flags"
+@@ -89,8 +98,8 @@
+ #define LAST_CPUPID_SHIFT 0
+ #endif
+ 
+-#if ZONES_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + KASAN_TAG_WIDTH + LAST_CPUPID_SHIFT \
+-	<= BITS_PER_LONG - NR_PAGEFLAGS
++#if ZONES_WIDTH + LRU_GEN_WIDTH + LRU_REFS_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + \
++	KASAN_TAG_WIDTH + LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
+ #define LAST_CPUPID_WIDTH LAST_CPUPID_SHIFT
+ #else
+ #define LAST_CPUPID_WIDTH 0
+@@ -100,8 +109,8 @@
+ #define LAST_CPUPID_NOT_IN_PAGE_FLAGS
+ #endif
+ 
+-#if ZONES_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + KASAN_TAG_WIDTH + LAST_CPUPID_WIDTH \
+-	> BITS_PER_LONG - NR_PAGEFLAGS
++#if ZONES_WIDTH + LRU_GEN_WIDTH + LRU_REFS_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + \
++	KASAN_TAG_WIDTH + LAST_CPUPID_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS
+ #error "Not enough bits in page flags"
+ #endif
+ 
+--- a/include/linux/page-flags.h
++++ b/include/linux/page-flags.h
+@@ -845,7 +845,7 @@ static inline void ClearPageSlabPfmemall
+ 	 1UL << PG_private	| 1UL << PG_private_2	|	\
+ 	 1UL << PG_writeback	| 1UL << PG_reserved	|	\
+ 	 1UL << PG_slab		| 1UL << PG_active 	|	\
+-	 1UL << PG_unevictable	| __PG_MLOCKED)
++	 1UL << PG_unevictable	| __PG_MLOCKED | LRU_GEN_MASK)
+ 
+ /*
+  * Flags checked when a page is prepped for return by the page allocator.
+@@ -856,7 +856,7 @@ static inline void ClearPageSlabPfmemall
+  * alloc-free cycle to prevent from reusing the page.
+  */
+ #define PAGE_FLAGS_CHECK_AT_PREP	\
+-	(PAGEFLAGS_MASK & ~__PG_HWPOISON)
++	((PAGEFLAGS_MASK & ~__PG_HWPOISON) | LRU_GEN_MASK | LRU_REFS_MASK)
+ 
+ #define PAGE_FLAGS_PRIVATE				\
+ 	(1UL << PG_private | 1UL << PG_private_2)
+--- a/include/linux/sched.h
++++ b/include/linux/sched.h
+@@ -911,6 +911,9 @@ struct task_struct {
+ #ifdef CONFIG_MEMCG
+ 	unsigned			in_user_fault:1;
+ #endif
++#ifdef CONFIG_LRU_GEN
++	unsigned			in_nonseq_fault:1;
++#endif
+ #ifdef CONFIG_COMPAT_BRK
+ 	unsigned			brk_randomized:1;
+ #endif
+--- a/kernel/bounds.c
++++ b/kernel/bounds.c
+@@ -22,6 +22,9 @@ int main(void)
+ 	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
+ #endif
+ 	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
++#ifdef CONFIG_LRU_GEN
++	DEFINE(LRU_GEN_WIDTH, order_base_2(CONFIG_NR_LRU_GENS + 1));
++#endif
+ 	/* End of constants */
+ 
+ 	return 0;
+--- a/kernel/cgroup/cgroup-internal.h
++++ b/kernel/cgroup/cgroup-internal.h
+@@ -165,7 +165,6 @@ struct cgroup_mgctx {
+ #define DEFINE_CGROUP_MGCTX(name)						\
+ 	struct cgroup_mgctx name = CGROUP_MGCTX_INIT(name)
+ 
+-extern struct mutex cgroup_mutex;
+ extern spinlock_t css_set_lock;
+ extern struct cgroup_subsys *cgroup_subsys[];
+ extern struct list_head cgroup_roots;
+--- a/mm/huge_memory.c
++++ b/mm/huge_memory.c
+@@ -2364,7 +2364,8 @@ static void __split_huge_page_tail(struc
+ #ifdef CONFIG_64BIT
+ 			 (1L << PG_arch_2) |
+ #endif
+-			 (1L << PG_dirty)));
++			 (1L << PG_dirty) |
++			 LRU_GEN_MASK | LRU_REFS_MASK));
+ 
+ 	/* ->mapping in first tail page is compound_mapcount */
+ 	VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
+--- a/mm/memcontrol.c
++++ b/mm/memcontrol.c
+@@ -5226,6 +5226,7 @@ static struct mem_cgroup *mem_cgroup_all
+ 	memcg->deferred_split_queue.split_queue_len = 0;
+ #endif
+ 	idr_replace(&mem_cgroup_idr, memcg, memcg->id.id);
++	lru_gen_init_memcg(memcg);
+ 	return memcg;
+ fail:
+ 	mem_cgroup_id_remove(memcg);
+--- a/mm/memory.c
++++ b/mm/memory.c
+@@ -4788,6 +4788,7 @@ vm_fault_t handle_mm_fault(struct vm_are
+ 			   unsigned int flags, struct pt_regs *regs)
+ {
+ 	vm_fault_t ret;
++	bool nonseq_fault = !(vma->vm_flags & VM_SEQ_READ);
+ 
+ 	__set_current_state(TASK_RUNNING);
+ 
+@@ -4809,11 +4810,17 @@ vm_fault_t handle_mm_fault(struct vm_are
+ 	if (flags & FAULT_FLAG_USER)
+ 		mem_cgroup_enter_user_fault();
+ 
++	if (nonseq_fault)
++		task_enter_nonseq_fault();
++
+ 	if (unlikely(is_vm_hugetlb_page(vma)))
+ 		ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
+ 	else
+ 		ret = __handle_mm_fault(vma, address, flags);
+ 
++	if (nonseq_fault)
++		task_exit_nonseq_fault();
++
+ 	if (flags & FAULT_FLAG_USER) {
+ 		mem_cgroup_exit_user_fault();
+ 		/*
+--- a/mm/mm_init.c
++++ b/mm/mm_init.c
+@@ -65,14 +65,16 @@ void __init mminit_verify_pageflags_layo
+ 
+ 	shift = 8 * sizeof(unsigned long);
+ 	width = shift - SECTIONS_WIDTH - NODES_WIDTH - ZONES_WIDTH
+-		- LAST_CPUPID_SHIFT - KASAN_TAG_WIDTH;
++		- LAST_CPUPID_SHIFT - KASAN_TAG_WIDTH - LRU_GEN_WIDTH - LRU_REFS_WIDTH;
+ 	mminit_dprintk(MMINIT_TRACE, "pageflags_layout_widths",
+-		"Section %d Node %d Zone %d Lastcpupid %d Kasantag %d Flags %d\n",
++		"Section %d Node %d Zone %d Lastcpupid %d Kasantag %d Gen %d Tier %d Flags %d\n",
+ 		SECTIONS_WIDTH,
+ 		NODES_WIDTH,
+ 		ZONES_WIDTH,
+ 		LAST_CPUPID_WIDTH,
+ 		KASAN_TAG_WIDTH,
++		LRU_GEN_WIDTH,
++		LRU_REFS_WIDTH,
+ 		NR_PAGEFLAGS);
+ 	mminit_dprintk(MMINIT_TRACE, "pageflags_layout_shifts",
+ 		"Section %d Node %d Zone %d Lastcpupid %d Kasantag %d\n",
+--- a/mm/page_alloc.c
++++ b/mm/page_alloc.c
+@@ -7411,6 +7411,7 @@ static void __meminit pgdat_init_interna
+ 
+ 	pgdat_page_ext_init(pgdat);
+ 	lruvec_init(&pgdat->__lruvec);
++	lru_gen_init_state(NULL, &pgdat->__lruvec);
+ }
+ 
+ static void __meminit zone_init_internals(struct zone *zone, enum zone_type idx, int nid,
+--- a/mm/swap.c
++++ b/mm/swap.c
+@@ -446,6 +446,11 @@ void lru_cache_add(struct page *page)
+ 	VM_BUG_ON_PAGE(PageActive(page) && PageUnevictable(page), page);
+ 	VM_BUG_ON_PAGE(PageLRU(page), page);
+ 
++	/* see the comment in lru_gen_add_page() */
++	if (lru_gen_enabled() && !PageUnevictable(page) &&
++	    task_in_nonseq_fault() && !(current->flags & PF_MEMALLOC))
++		SetPageActive(page);
++
+ 	get_page(page);
+ 	local_lock(&lru_pvecs.lock);
+ 	pvec = this_cpu_ptr(&lru_pvecs.lru_add);
+@@ -547,7 +552,7 @@ static void lru_deactivate_file_fn(struc
+ 
+ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec)
+ {
+-	if (PageActive(page) && !PageUnevictable(page)) {
++	if (!PageUnevictable(page) && (PageActive(page) || lru_gen_enabled())) {
+ 		int nr_pages = thp_nr_pages(page);
+ 
+ 		del_page_from_lru_list(page, lruvec);
+@@ -661,7 +666,7 @@ void deactivate_file_page(struct page *p
+  */
+ void deactivate_page(struct page *page)
+ {
+-	if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
++	if (PageLRU(page) && !PageUnevictable(page) && (PageActive(page) || lru_gen_enabled())) {
+ 		struct pagevec *pvec;
+ 
+ 		local_lock(&lru_pvecs.lock);
+--- a/mm/swapfile.c
++++ b/mm/swapfile.c
+@@ -2688,6 +2688,7 @@ SYSCALL_DEFINE1(swapoff, const char __us
+ 	err = 0;
+ 	atomic_inc(&proc_poll_event);
+ 	wake_up_interruptible(&proc_poll_wait);
++	lru_gen_change_state(false, false, true);
+ 
+ out_dput:
+ 	filp_close(victim, NULL);
+@@ -3349,6 +3350,7 @@ SYSCALL_DEFINE2(swapon, const char __use
+ 	mutex_unlock(&swapon_mutex);
+ 	atomic_inc(&proc_poll_event);
+ 	wake_up_interruptible(&proc_poll_wait);
++	lru_gen_change_state(true, false, true);
+ 
+ 	error = 0;
+ 	goto out;
+--- a/mm/vmscan.c
++++ b/mm/vmscan.c
+@@ -50,6 +50,7 @@
+ #include <linux/printk.h>
+ #include <linux/dax.h>
+ #include <linux/psi.h>
++#include <linux/memory.h>
+ 
+ #include <asm/tlbflush.h>
+ #include <asm/div64.h>
+@@ -2880,6 +2881,273 @@ static bool can_age_anon_pages(struct pg
+ 	return can_demote(pgdat->node_id, sc);
+ }
+ 
++#ifdef CONFIG_LRU_GEN
++
++/******************************************************************************
++ *                          shorthand helpers
++ ******************************************************************************/
++
++#define for_each_gen_type_zone(gen, type, zone)				\
++	for ((gen) = 0; (gen) < MAX_NR_GENS; (gen)++)			\
++		for ((type) = 0; (type) < ANON_AND_FILE; (type)++)	\
++			for ((zone) = 0; (zone) < MAX_NR_ZONES; (zone)++)
++
++static int page_lru_gen(struct page *page)
++{
++	unsigned long flags = READ_ONCE(page->flags);
++
++	return ((flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
++}
++
++static struct lruvec *get_lruvec(int nid, struct mem_cgroup *memcg)
++{
++	struct pglist_data *pgdat = NODE_DATA(nid);
++
++#ifdef CONFIG_MEMCG
++	if (memcg) {
++		struct lruvec *lruvec = &memcg->nodeinfo[nid]->lruvec;
++
++		if (lruvec->pgdat != pgdat)
++			lruvec->pgdat = pgdat;
++
++		return lruvec;
++	}
++#endif
++	return pgdat ? &pgdat->__lruvec : NULL;
++}
++
++static int get_nr_gens(struct lruvec *lruvec, int type)
++{
++	return lruvec->evictable.max_seq - lruvec->evictable.min_seq[type] + 1;
++}
++
++static bool __maybe_unused seq_is_valid(struct lruvec *lruvec)
++{
++	return get_nr_gens(lruvec, 1) >= MIN_NR_GENS &&
++	       get_nr_gens(lruvec, 1) <= get_nr_gens(lruvec, 0) &&
++	       get_nr_gens(lruvec, 0) <= MAX_NR_GENS;
++}
++
++/******************************************************************************
++ *                          state change
++ ******************************************************************************/
++
++#ifdef CONFIG_LRU_GEN_ENABLED
++DEFINE_STATIC_KEY_TRUE(lru_gen_static_key);
++#else
++DEFINE_STATIC_KEY_FALSE(lru_gen_static_key);
++#endif
++
++static int lru_gen_nr_swapfiles;
++
++static bool __maybe_unused state_is_valid(struct lruvec *lruvec)
++{
++	int gen, type, zone;
++	enum lru_list lru;
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	for_each_evictable_lru(lru) {
++		type = is_file_lru(lru);
++
++		if (lrugen->enabled[type] && !list_empty(&lruvec->lists[lru]))
++			return false;
++	}
++
++	for_each_gen_type_zone(gen, type, zone) {
++		if (!lrugen->enabled[type] && !list_empty(&lrugen->lists[gen][type][zone]))
++			return false;
++
++		/* unlikely but not a bug when reset_batch_size() is pending */
++		VM_WARN_ON(!lrugen->enabled[type] && lrugen->sizes[gen][type][zone]);
++	}
++
++	return true;
++}
++
++static bool fill_lists(struct lruvec *lruvec)
++{
++	enum lru_list lru;
++	int remaining = MAX_BATCH_SIZE;
++
++	for_each_evictable_lru(lru) {
++		int type = is_file_lru(lru);
++		bool active = is_active_lru(lru);
++		struct list_head *head = &lruvec->lists[lru];
++
++		if (!lruvec->evictable.enabled[type])
++			continue;
++
++		while (!list_empty(head)) {
++			bool success;
++			struct page *page = lru_to_page(head);
++
++			VM_BUG_ON_PAGE(PageTail(page), page);
++			VM_BUG_ON_PAGE(PageUnevictable(page), page);
++			VM_BUG_ON_PAGE(PageActive(page) != active, page);
++			VM_BUG_ON_PAGE(page_is_file_lru(page) != type, page);
++			VM_BUG_ON_PAGE(page_lru_gen(page) < MAX_NR_GENS, page);
++
++			prefetchw_prev_lru_page(page, head, flags);
++
++			del_page_from_lru_list(page, lruvec);
++			success = lru_gen_add_page(page, lruvec, false);
++			VM_BUG_ON(!success);
++
++			if (!--remaining)
++				return false;
++		}
++	}
++
++	return true;
++}
++
++static bool drain_lists(struct lruvec *lruvec)
++{
++	int gen, type, zone;
++	int remaining = MAX_BATCH_SIZE;
++
++	for_each_gen_type_zone(gen, type, zone) {
++		struct list_head *head = &lruvec->evictable.lists[gen][type][zone];
++
++		if (lruvec->evictable.enabled[type])
++			continue;
++
++		while (!list_empty(head)) {
++			bool success;
++			struct page *page = lru_to_page(head);
++
++			VM_BUG_ON_PAGE(PageTail(page), page);
++			VM_BUG_ON_PAGE(PageUnevictable(page), page);
++			VM_BUG_ON_PAGE(PageActive(page), page);
++			VM_BUG_ON_PAGE(page_is_file_lru(page) != type, page);
++			VM_BUG_ON_PAGE(page_zonenum(page) != zone, page);
++
++			prefetchw_prev_lru_page(page, head, flags);
++
++			success = lru_gen_del_page(page, lruvec, false);
++			VM_BUG_ON(!success);
++			add_page_to_lru_list(page, lruvec);
++
++			if (!--remaining)
++				return false;
++		}
++	}
++
++	return true;
++}
++
++/*
++ * For file page tracking, we enable/disable it according to the main switch.
++ * For anon page tracking, we only enabled it when the main switch is on and
++ * there is at least one swapfile; we disable it when there are no swapfiles
++ * regardless of the value of the main switch. Otherwise, we will eventually
++ * reach the max size of the sliding window and have to call inc_min_seq().
++ */
++void lru_gen_change_state(bool enable, bool main, bool swap)
++{
++	static DEFINE_MUTEX(state_mutex);
++
++	struct mem_cgroup *memcg;
++
++	mem_hotplug_begin();
++	cgroup_lock();
++	mutex_lock(&state_mutex);
++
++	if (swap) {
++		if (enable)
++			swap = !lru_gen_nr_swapfiles++;
++		else
++			swap = !--lru_gen_nr_swapfiles;
++	}
++
++	if (main && enable != lru_gen_enabled()) {
++		if (enable)
++			static_branch_enable(&lru_gen_static_key);
++		else
++			static_branch_disable(&lru_gen_static_key);
++	} else if (!swap || !lru_gen_enabled())
++		goto unlock;
++
++	memcg = mem_cgroup_iter(NULL, NULL, NULL);
++	do {
++		int nid;
++
++		for_each_node(nid) {
++			struct lruvec *lruvec = get_lruvec(nid, memcg);
++
++			if (!lruvec)
++				continue;
++
++			spin_lock_irq(&lruvec->lru_lock);
++
++			VM_BUG_ON(!seq_is_valid(lruvec));
++			VM_BUG_ON(!state_is_valid(lruvec));
++
++			lruvec->evictable.enabled[0] = lru_gen_enabled() && lru_gen_nr_swapfiles;
++			lruvec->evictable.enabled[1] = lru_gen_enabled();
++
++			while (!(enable ? fill_lists(lruvec) : drain_lists(lruvec))) {
++				spin_unlock_irq(&lruvec->lru_lock);
++				cond_resched();
++				spin_lock_irq(&lruvec->lru_lock);
++			}
++
++			spin_unlock_irq(&lruvec->lru_lock);
++		}
++
++		cond_resched();
++	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
++unlock:
++	mutex_unlock(&state_mutex);
++	cgroup_unlock();
++	mem_hotplug_done();
++}
++
++/******************************************************************************
++ *                          initialization
++ ******************************************************************************/
++
++void lru_gen_init_state(struct mem_cgroup *memcg, struct lruvec *lruvec)
++{
++	int i;
++	int gen, type, zone;
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	lrugen->max_seq = MIN_NR_GENS + 1;
++	lrugen->enabled[0] = lru_gen_enabled() && lru_gen_nr_swapfiles;
++	lrugen->enabled[1] = lru_gen_enabled();
++
++	for (i = 0; i <= MIN_NR_GENS + 1; i++)
++		lrugen->timestamps[i] = jiffies;
++
++	for_each_gen_type_zone(gen, type, zone)
++		INIT_LIST_HEAD(&lrugen->lists[gen][type][zone]);
++}
++
++#ifdef CONFIG_MEMCG
++void lru_gen_init_memcg(struct mem_cgroup *memcg)
++{
++	int nid;
++
++	for_each_node(nid) {
++		struct lruvec *lruvec = get_lruvec(nid, memcg);
++
++		lru_gen_init_state(memcg, lruvec);
++	}
++}
++#endif
++
++static int __init init_lru_gen(void)
++{
++	BUILD_BUG_ON(MIN_NR_GENS + 1 >= MAX_NR_GENS);
++	BUILD_BUG_ON(BIT(LRU_GEN_WIDTH) <= MAX_NR_GENS);
++
++	return 0;
++};
++late_initcall(init_lru_gen);
++
++#endif /* CONFIG_LRU_GEN */
++
+ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
+ {
+ 	unsigned long nr[NR_LRU_LISTS];

target/linux/generic/pending-5.15/020-04-mm-multigenerational-lru-mm_struct-list.patch

@@ -0,0 +1,760 @@
+From 534bcc4a0bb5b24600891ce793f0295a142e9dae Mon Sep 17 00:00:00 2001
+From: Yu Zhao <[email protected]>
+Date: Mon, 5 Apr 2021 04:17:41 -0600
+Subject: [PATCH 05/10] mm: multigenerational lru: mm_struct list
+
+To scan PTEs for accessed pages, a mm_struct list is maintained for
+each memcg. When multiple threads traverse the same memcg->mm_list,
+each of them gets a unique mm_struct and therefore they can run
+walk_page_range() concurrently to reach page tables of all processes
+of this memcg.
+
+This infrastructure also provides the following optimizations:
+  1) it allows walkers to skip processes that have been sleeping since
+  the last walk by tracking the usage of mm_struct between context
+  switches.
+  2) it allows walkers to add interesting items they find during a
+  walk to a Bloom filter so that they can skip uninteresting items
+  during the next walk by testing whether an item is in this Bloom
+  filter.
+
+Signed-off-by: Yu Zhao <[email protected]>
+Tested-by: Konstantin Kharlamov <[email protected]>
+Change-Id: I25d9eda8c6bdc7c3653b9f210a159d6c247c81e8
+---
+ fs/exec.c                  |   2 +
+ include/linux/memcontrol.h |   4 +
+ include/linux/mm_inline.h  |   6 +
+ include/linux/mm_types.h   |  75 +++++++++
+ include/linux/mmzone.h     |  63 +++++++
+ kernel/exit.c              |   1 +
+ kernel/fork.c              |   9 +
+ kernel/sched/core.c        |   1 +
+ mm/memcontrol.c            |  25 +++
+ mm/vmscan.c                | 331 +++++++++++++++++++++++++++++++++++++
+ 10 files changed, 517 insertions(+)
+
+--- a/fs/exec.c
++++ b/fs/exec.c
+@@ -1013,6 +1013,7 @@ static int exec_mmap(struct mm_struct *m
+ 	active_mm = tsk->active_mm;
+ 	tsk->active_mm = mm;
+ 	tsk->mm = mm;
++	lru_gen_add_mm(mm);
+ 	/*
+ 	 * This prevents preemption while active_mm is being loaded and
+ 	 * it and mm are being updated, which could cause problems for
+@@ -1023,6 +1024,7 @@ static int exec_mmap(struct mm_struct *m
+ 	if (!IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM))
+ 		local_irq_enable();
+ 	activate_mm(active_mm, mm);
++	lru_gen_activate_mm(mm);
+ 	if (IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM))
+ 		local_irq_enable();
+ 	tsk->mm->vmacache_seqnum = 0;
+--- a/include/linux/memcontrol.h
++++ b/include/linux/memcontrol.h
+@@ -348,6 +348,10 @@ struct mem_cgroup {
+ 	struct deferred_split deferred_split_queue;
+ #endif
+ 
++#ifdef CONFIG_LRU_GEN
++	struct lru_gen_mm_list mm_list;
++#endif
++
+ 	struct mem_cgroup_per_node *nodeinfo[];
+ };
+ 
+--- a/include/linux/mm_inline.h
++++ b/include/linux/mm_inline.h
+@@ -100,6 +100,12 @@ static inline int lru_gen_from_seq(unsig
+ 	return seq % MAX_NR_GENS;
+ }
+ 
++/* Return a proper index regardless whether we keep stats for historical generations. */
++static inline int lru_hist_from_seq(unsigned long seq)
++{
++	return seq % NR_HIST_GENS;
++}
++
+ /* The youngest and the second youngest generations are counted as active. */
+ static inline bool lru_gen_is_active(struct lruvec *lruvec, int gen)
+ {
+--- a/include/linux/mm_types.h
++++ b/include/linux/mm_types.h
+@@ -3,6 +3,7 @@
+ #define _LINUX_MM_TYPES_H
+ 
+ #include <linux/mm_types_task.h>
++#include <linux/sched.h>
+ 
+ #include <linux/auxvec.h>
+ #include <linux/list.h>
+@@ -15,6 +16,8 @@
+ #include <linux/page-flags-layout.h>
+ #include <linux/workqueue.h>
+ #include <linux/seqlock.h>
++#include <linux/nodemask.h>
++#include <linux/mmdebug.h>
+ 
+ #include <asm/mmu.h>
+ 
+@@ -580,6 +583,18 @@ struct mm_struct {
+ #ifdef CONFIG_IOMMU_SUPPORT
+ 		u32 pasid;
+ #endif
++#ifdef CONFIG_LRU_GEN
++		struct {
++			/* the node of a global or per-memcg mm_struct list */
++			struct list_head list;
++#ifdef CONFIG_MEMCG
++			/* points to the memcg of the owner task above */
++			struct mem_cgroup *memcg;
++#endif
++			/* whether this mm_struct has been used since the last walk */
++			nodemask_t nodes;
++		} lrugen;
++#endif /* CONFIG_LRU_GEN */
+ 	} __randomize_layout;
+ 
+ 	/*
+@@ -606,6 +621,66 @@ static inline cpumask_t *mm_cpumask(stru
+ 	return (struct cpumask *)&mm->cpu_bitmap;
+ }
+ 
++#ifdef CONFIG_LRU_GEN
++
++struct lru_gen_mm_list {
++	/* a global or per-memcg mm_struct list */
++	struct list_head fifo;
++	/* protects the list above */
++	spinlock_t lock;
++};
++
++void lru_gen_add_mm(struct mm_struct *mm);
++void lru_gen_del_mm(struct mm_struct *mm);
++#ifdef CONFIG_MEMCG
++void lru_gen_migrate_mm(struct mm_struct *mm);
++#endif
++
++static inline void lru_gen_init_mm(struct mm_struct *mm)
++{
++	INIT_LIST_HEAD(&mm->lrugen.list);
++#ifdef CONFIG_MEMCG
++	mm->lrugen.memcg = NULL;
++#endif
++	nodes_clear(mm->lrugen.nodes);
++}
++
++/* Track the usage of each mm_struct so that we can skip inactive ones. */
++static inline void lru_gen_activate_mm(struct mm_struct *mm)
++{
++	/* unlikely but not a bug when racing with lru_gen_migrate_mm() */
++	VM_WARN_ON(list_empty(&mm->lrugen.list));
++
++	if (!(current->flags & PF_KTHREAD) && !nodes_full(mm->lrugen.nodes))
++		nodes_setall(mm->lrugen.nodes);
++}
++
++#else /* !CONFIG_LRU_GEN */
++
++static inline void lru_gen_add_mm(struct mm_struct *mm)
++{
++}
++
++static inline void lru_gen_del_mm(struct mm_struct *mm)
++{
++}
++
++#ifdef CONFIG_MEMCG
++static inline void lru_gen_migrate_mm(struct mm_struct *mm)
++{
++}
++#endif
++
++static inline void lru_gen_init_mm(struct mm_struct *mm)
++{
++}
++
++static inline void lru_gen_activate_mm(struct mm_struct *mm)
++{
++}
++
++#endif /* CONFIG_LRU_GEN */
++
+ struct mmu_gather;
+ extern void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm);
+ extern void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm);
+--- a/include/linux/mmzone.h
++++ b/include/linux/mmzone.h
+@@ -318,6 +318,13 @@ struct lruvec;
+ #define MIN_NR_GENS		2
+ #define MAX_NR_GENS		((unsigned int)CONFIG_NR_LRU_GENS)
+ 
++/* Whether to keep stats for historical generations. */
++#ifdef CONFIG_LRU_GEN_STATS
++#define NR_HIST_GENS		((unsigned int)CONFIG_NR_LRU_GENS)
++#else
++#define NR_HIST_GENS		1U
++#endif
++
+ struct lrugen {
+ 	/* the aging increments the max generation number */
+ 	unsigned long max_seq;
+@@ -333,13 +340,63 @@ struct lrugen {
+ 	bool enabled[ANON_AND_FILE];
+ };
+ 
++enum {
++	MM_LEAF_TOTAL,		/* total leaf entries */
++	MM_LEAF_OLD,		/* old leaf entries */
++	MM_LEAF_YOUNG,		/* young leaf entries */
++	MM_NONLEAF_TOTAL,	/* total non-leaf entries */
++	MM_NONLEAF_PREV,	/* previously worthy non-leaf entries */
++	MM_NONLEAF_CUR,		/* currently worthy non-leaf entries */
++	NR_MM_STATS
++};
++
++/* mnemonic codes for the stats above */
++#define MM_STAT_CODES		"toydpc"
++
++/* double buffering bloom filters */
++#define NR_BLOOM_FILTERS	2
++
++struct lru_gen_mm_walk {
++	/* set to max_seq after each round of walk */
++	unsigned long seq;
++	/* the next mm_struct on the list to walk */
++	struct list_head *head;
++	/* the first mm_struct never walked before */
++	struct list_head *tail;
++	/* to wait for the last walker to finish */
++	struct wait_queue_head wait;
++	/* bloom filters flip after each round of walk */
++	unsigned long *filters[NR_BLOOM_FILTERS];
++	/* page table stats for debugging */
++	unsigned long stats[NR_HIST_GENS][NR_MM_STATS];
++	/* the number of concurrent walkers */
++	int nr_walkers;
++};
++
++#define MIN_BATCH_SIZE		64
+ #define MAX_BATCH_SIZE		8192
+ 
++struct mm_walk_args {
++	struct mem_cgroup *memcg;
++	unsigned long max_seq;
++	unsigned long start_pfn;
++	unsigned long end_pfn;
++	unsigned long next_addr;
++	unsigned long bitmap[BITS_TO_LONGS(MIN_BATCH_SIZE)];
++	int node_id;
++	int swappiness;
++	int batch_size;
++	int nr_pages[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
++	int mm_stats[NR_MM_STATS];
++	bool use_filter;
++};
++
+ void lru_gen_init_state(struct mem_cgroup *memcg, struct lruvec *lruvec);
+ void lru_gen_change_state(bool enable, bool main, bool swap);
+ 
+ #ifdef CONFIG_MEMCG
+ void lru_gen_init_memcg(struct mem_cgroup *memcg);
++void lru_gen_free_memcg(struct mem_cgroup *memcg);
+ #endif
+ 
+ #else /* !CONFIG_LRU_GEN */
+@@ -356,6 +413,10 @@ static inline void lru_gen_change_state(
+ static inline void lru_gen_init_memcg(struct mem_cgroup *memcg)
+ {
+ }
++
++static inline void lru_gen_free_memcg(struct mem_cgroup *memcg)
++{
++}
+ #endif
+ 
+ #endif /* CONFIG_LRU_GEN */
+@@ -380,6 +441,8 @@ struct lruvec {
+ #ifdef CONFIG_LRU_GEN
+ 	/* unevictable pages are on LRU_UNEVICTABLE */
+ 	struct lrugen			evictable;
++	/* state for mm list and page table walks */
++	struct lru_gen_mm_walk		mm_walk;
+ #endif
+ #ifdef CONFIG_MEMCG
+ 	struct pglist_data *pgdat;
+--- a/kernel/exit.c
++++ b/kernel/exit.c
+@@ -422,6 +422,7 @@ assign_new_owner:
+ 		goto retry;
+ 	}
+ 	WRITE_ONCE(mm->owner, c);
++	lru_gen_migrate_mm(mm);
+ 	task_unlock(c);
+ 	put_task_struct(c);
+ }
+--- a/kernel/fork.c
++++ b/kernel/fork.c
+@@ -1080,6 +1080,7 @@ static struct mm_struct *mm_init(struct
+ 		goto fail_nocontext;
+ 
+ 	mm->user_ns = get_user_ns(user_ns);
++	lru_gen_init_mm(mm);
+ 	return mm;
+ 
+ fail_nocontext:
+@@ -1122,6 +1123,7 @@ static inline void __mmput(struct mm_str
+ 	}
+ 	if (mm->binfmt)
+ 		module_put(mm->binfmt->module);
++	lru_gen_del_mm(mm);
+ 	mmdrop(mm);
+ }
+ 
+@@ -2616,6 +2618,13 @@ pid_t kernel_clone(struct kernel_clone_a
+ 		get_task_struct(p);
+ 	}
+ 
++	if (IS_ENABLED(CONFIG_LRU_GEN) && !(clone_flags & CLONE_VM)) {
++		/* lock the task to synchronize with memcg migration */
++		task_lock(p);
++		lru_gen_add_mm(p->mm);
++		task_unlock(p);
++	}
++
+ 	wake_up_new_task(p);
+ 
+ 	/* forking complete and child started to run, tell ptracer */
+--- a/kernel/sched/core.c
++++ b/kernel/sched/core.c
+@@ -4978,6 +4978,7 @@ context_switch(struct rq *rq, struct tas
+ 		 * finish_task_switch()'s mmdrop().
+ 		 */
+ 		switch_mm_irqs_off(prev->active_mm, next->mm, next);
++		lru_gen_activate_mm(next->mm);
+ 
+ 		if (!prev->mm) {                        // from kernel
+ 			/* will mmdrop() in finish_task_switch(). */
+--- a/mm/memcontrol.c
++++ b/mm/memcontrol.c
+@@ -5163,6 +5163,7 @@ static void __mem_cgroup_free(struct mem
+ 
+ static void mem_cgroup_free(struct mem_cgroup *memcg)
+ {
++	lru_gen_free_memcg(memcg);
+ 	memcg_wb_domain_exit(memcg);
+ 	__mem_cgroup_free(memcg);
+ }
+@@ -6195,6 +6196,29 @@ static void mem_cgroup_move_task(void)
+ }
+ #endif
+ 
++#ifdef CONFIG_LRU_GEN
++static void mem_cgroup_attach(struct cgroup_taskset *tset)
++{
++	struct cgroup_subsys_state *css;
++	struct task_struct *task = NULL;
++
++	cgroup_taskset_for_each_leader(task, css, tset)
++		break;
++
++	if (!task)
++		return;
++
++	task_lock(task);
++	if (task->mm && task->mm->owner == task)
++		lru_gen_migrate_mm(task->mm);
++	task_unlock(task);
++}
++#else
++static void mem_cgroup_attach(struct cgroup_taskset *tset)
++{
++}
++#endif /* CONFIG_LRU_GEN */
++
+ static int seq_puts_memcg_tunable(struct seq_file *m, unsigned long value)
+ {
+ 	if (value == PAGE_COUNTER_MAX)
+@@ -6538,6 +6562,7 @@ struct cgroup_subsys memory_cgrp_subsys
+ 	.css_reset = mem_cgroup_css_reset,
+ 	.css_rstat_flush = mem_cgroup_css_rstat_flush,
+ 	.can_attach = mem_cgroup_can_attach,
++	.attach = mem_cgroup_attach,
+ 	.cancel_attach = mem_cgroup_cancel_attach,
+ 	.post_attach = mem_cgroup_move_task,
+ 	.dfl_cftypes = memory_files,
+--- a/mm/vmscan.c
++++ b/mm/vmscan.c
+@@ -2929,6 +2929,306 @@ static bool __maybe_unused seq_is_valid(
+ }
+ 
+ /******************************************************************************
++ *                          mm_struct list
++ ******************************************************************************/
++
++static struct lru_gen_mm_list *get_mm_list(struct mem_cgroup *memcg)
++{
++	static struct lru_gen_mm_list mm_list = {
++		.fifo = LIST_HEAD_INIT(mm_list.fifo),
++		.lock = __SPIN_LOCK_UNLOCKED(mm_list.lock),
++	};
++
++#ifdef CONFIG_MEMCG
++	if (memcg)
++		return &memcg->mm_list;
++#endif
++	return &mm_list;
++}
++
++void lru_gen_add_mm(struct mm_struct *mm)
++{
++	int nid;
++	struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm);
++	struct lru_gen_mm_list *mm_list = get_mm_list(memcg);
++
++	VM_BUG_ON_MM(!list_empty(&mm->lrugen.list), mm);
++#ifdef CONFIG_MEMCG
++	VM_BUG_ON_MM(mm->lrugen.memcg, mm);
++	mm->lrugen.memcg = memcg;
++#endif
++	spin_lock(&mm_list->lock);
++
++	list_add_tail(&mm->lrugen.list, &mm_list->fifo);
++
++	for_each_node(nid) {
++		struct lruvec *lruvec = get_lruvec(nid, memcg);
++
++		if (!lruvec)
++			continue;
++
++		if (lruvec->mm_walk.tail == &mm_list->fifo)
++			lruvec->mm_walk.tail = lruvec->mm_walk.tail->prev;
++	}
++
++	spin_unlock(&mm_list->lock);
++}
++
++void lru_gen_del_mm(struct mm_struct *mm)
++{
++	int nid;
++	struct lru_gen_mm_list *mm_list;
++	struct mem_cgroup *memcg = NULL;
++
++	if (list_empty(&mm->lrugen.list))
++		return;
++
++#ifdef CONFIG_MEMCG
++	memcg = mm->lrugen.memcg;
++#endif
++	mm_list = get_mm_list(memcg);
++
++	spin_lock(&mm_list->lock);
++
++	for_each_node(nid) {
++		struct lruvec *lruvec = get_lruvec(nid, memcg);
++
++		if (!lruvec)
++			continue;
++
++		if (lruvec->mm_walk.tail == &mm->lrugen.list)
++			lruvec->mm_walk.tail = lruvec->mm_walk.tail->next;
++
++		if (lruvec->mm_walk.head != &mm->lrugen.list)
++			continue;
++
++		lruvec->mm_walk.head = lruvec->mm_walk.head->next;
++		if (lruvec->mm_walk.head == &mm_list->fifo)
++			WRITE_ONCE(lruvec->mm_walk.seq, lruvec->mm_walk.seq + 1);
++	}
++
++	list_del_init(&mm->lrugen.list);
++
++	spin_unlock(&mm_list->lock);
++
++#ifdef CONFIG_MEMCG
++	mem_cgroup_put(mm->lrugen.memcg);
++	mm->lrugen.memcg = NULL;
++#endif
++}
++
++#ifdef CONFIG_MEMCG
++void lru_gen_migrate_mm(struct mm_struct *mm)
++{
++	struct mem_cgroup *memcg;
++
++	lockdep_assert_held(&mm->owner->alloc_lock);
++
++	if (mem_cgroup_disabled())
++		return;
++
++	rcu_read_lock();
++	memcg = mem_cgroup_from_task(mm->owner);
++	rcu_read_unlock();
++	if (memcg == mm->lrugen.memcg)
++		return;
++
++	VM_BUG_ON_MM(!mm->lrugen.memcg, mm);
++	VM_BUG_ON_MM(list_empty(&mm->lrugen.list), mm);
++
++	lru_gen_del_mm(mm);
++	lru_gen_add_mm(mm);
++}
++#endif
++
++#define BLOOM_FILTER_SHIFT	15
++
++static inline int filter_gen_from_seq(unsigned long seq)
++{
++	return seq % NR_BLOOM_FILTERS;
++}
++
++static void get_item_key(void *item, int *key)
++{
++	u32 hash = hash_ptr(item, BLOOM_FILTER_SHIFT * 2);
++
++	BUILD_BUG_ON(BLOOM_FILTER_SHIFT * 2 > BITS_PER_TYPE(u32));
++
++	key[0] = hash & (BIT(BLOOM_FILTER_SHIFT) - 1);
++	key[1] = hash >> BLOOM_FILTER_SHIFT;
++}
++
++static void clear_bloom_filter(struct lruvec *lruvec, unsigned long seq)
++{
++	unsigned long *filter;
++	int gen = filter_gen_from_seq(seq);
++
++	lockdep_assert_held(&get_mm_list(lruvec_memcg(lruvec))->lock);
++
++	filter = lruvec->mm_walk.filters[gen];
++	if (filter) {
++		bitmap_clear(filter, 0, BIT(BLOOM_FILTER_SHIFT));
++		return;
++	}
++
++	filter = bitmap_zalloc(BIT(BLOOM_FILTER_SHIFT), GFP_ATOMIC);
++	WRITE_ONCE(lruvec->mm_walk.filters[gen], filter);
++}
++
++static void set_bloom_filter(struct lruvec *lruvec, unsigned long seq, void *item)
++{
++	int key[2];
++	unsigned long *filter;
++	int gen = filter_gen_from_seq(seq);
++
++	filter = READ_ONCE(lruvec->mm_walk.filters[gen]);
++	if (!filter)
++		return;
++
++	get_item_key(item, key);
++
++	if (!test_bit(key[0], filter))
++		set_bit(key[0], filter);
++	if (!test_bit(key[1], filter))
++		set_bit(key[1], filter);
++}
++
++static bool test_bloom_filter(struct lruvec *lruvec, unsigned long seq, void *item)
++{
++	int key[2];
++	unsigned long *filter;
++	int gen = filter_gen_from_seq(seq);
++
++	filter = READ_ONCE(lruvec->mm_walk.filters[gen]);
++	if (!filter)
++		return false;
++
++	get_item_key(item, key);
++
++	return test_bit(key[0], filter) && test_bit(key[1], filter);
++}
++
++static void reset_mm_stats(struct lruvec *lruvec, bool last, struct mm_walk_args *args)
++{
++	int i;
++	int hist = lru_hist_from_seq(args->max_seq);
++
++	lockdep_assert_held(&get_mm_list(lruvec_memcg(lruvec))->lock);
++
++	for (i = 0; i < NR_MM_STATS; i++) {
++		WRITE_ONCE(lruvec->mm_walk.stats[hist][i],
++			   lruvec->mm_walk.stats[hist][i] + args->mm_stats[i]);
++		args->mm_stats[i] = 0;
++	}
++
++	if (!last || NR_HIST_GENS == 1)
++		return;
++
++	hist = lru_hist_from_seq(args->max_seq + 1);
++	for (i = 0; i < NR_MM_STATS; i++)
++		WRITE_ONCE(lruvec->mm_walk.stats[hist][i], 0);
++}
++
++static bool should_skip_mm(struct mm_struct *mm, struct mm_walk_args *args)
++{
++	int type;
++	unsigned long size = 0;
++
++	if (cpumask_empty(mm_cpumask(mm)) && !node_isset(args->node_id, mm->lrugen.nodes))
++		return true;
++
++	if (mm_is_oom_victim(mm))
++		return true;
++
++	for (type = !args->swappiness; type < ANON_AND_FILE; type++) {
++		size += type ? get_mm_counter(mm, MM_FILEPAGES) :
++			       get_mm_counter(mm, MM_ANONPAGES) +
++			       get_mm_counter(mm, MM_SHMEMPAGES);
++	}
++
++	if (size < MIN_BATCH_SIZE)
++		return true;
++
++	if (!mmget_not_zero(mm))
++		return true;
++
++	node_clear(args->node_id, mm->lrugen.nodes);
++
++	return false;
++}
++
++/* To support multiple walkers that concurrently walk an mm_struct list. */
++static bool get_next_mm(struct lruvec *lruvec, struct mm_walk_args *args,
++			struct mm_struct **iter)
++{
++	bool first = false;
++	bool last = true;
++	struct mm_struct *mm = NULL;
++	struct lru_gen_mm_walk *mm_walk = &lruvec->mm_walk;
++	struct lru_gen_mm_list *mm_list = get_mm_list(args->memcg);
++
++	if (*iter)
++		mmput_async(*iter);
++	else if (args->max_seq <= READ_ONCE(mm_walk->seq))
++		return false;
++
++	spin_lock(&mm_list->lock);
++
++	VM_BUG_ON(args->max_seq > mm_walk->seq + 1);
++	VM_BUG_ON(*iter && args->max_seq < mm_walk->seq);
++	VM_BUG_ON(*iter && !mm_walk->nr_walkers);
++
++	if (args->max_seq <= mm_walk->seq) {
++		if (!*iter)
++			last = false;
++		goto done;
++	}
++
++	if (mm_walk->head == &mm_list->fifo) {
++		VM_BUG_ON(mm_walk->nr_walkers);
++		mm_walk->head = mm_walk->head->next;
++		first = true;
++	}
++
++	while (!mm && mm_walk->head != &mm_list->fifo) {
++		mm = list_entry(mm_walk->head, struct mm_struct, lrugen.list);
++
++		mm_walk->head = mm_walk->head->next;
++
++		if (mm_walk->tail == &mm->lrugen.list) {
++			mm_walk->tail = mm_walk->tail->next;
++			args->use_filter = false;
++		}
++
++		if (should_skip_mm(mm, args))
++			mm = NULL;
++	}
++
++	if (mm_walk->head == &mm_list->fifo)
++		WRITE_ONCE(mm_walk->seq, mm_walk->seq + 1);
++done:
++	if (*iter && !mm)
++		mm_walk->nr_walkers--;
++	if (!*iter && mm)
++		mm_walk->nr_walkers++;
++
++	if (mm_walk->nr_walkers)
++		last = false;
++
++	if (mm && first)
++		clear_bloom_filter(lruvec, args->max_seq + 1);
++
++	if (*iter || last)
++		reset_mm_stats(lruvec, last, args);
++
++	spin_unlock(&mm_list->lock);
++
++	*iter = mm;
++
++	return last;
++}
++
++/******************************************************************************
+  *                          state change
+  ******************************************************************************/
+ 
+@@ -3112,6 +3412,7 @@ void lru_gen_init_state(struct mem_cgrou
+ 	int i;
+ 	int gen, type, zone;
+ 	struct lrugen *lrugen = &lruvec->evictable;
++	struct lru_gen_mm_list *mm_list = get_mm_list(memcg);
+ 
+ 	lrugen->max_seq = MIN_NR_GENS + 1;
+ 	lrugen->enabled[0] = lru_gen_enabled() && lru_gen_nr_swapfiles;
+@@ -3122,6 +3423,17 @@ void lru_gen_init_state(struct mem_cgrou
+ 
+ 	for_each_gen_type_zone(gen, type, zone)
+ 		INIT_LIST_HEAD(&lrugen->lists[gen][type][zone]);
++
++	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG) && !memcg)
++		spin_lock(&mm_list->lock);
++
++	lruvec->mm_walk.seq = MIN_NR_GENS;
++	lruvec->mm_walk.head = &mm_list->fifo;
++	lruvec->mm_walk.tail = &mm_list->fifo;
++	init_waitqueue_head(&lruvec->mm_walk.wait);
++
++	if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG) && !memcg)
++		spin_unlock(&mm_list->lock);
+ }
+ 
+ #ifdef CONFIG_MEMCG
+@@ -3129,18 +3441,37 @@ void lru_gen_init_memcg(struct mem_cgrou
+ {
+ 	int nid;
+ 
++	INIT_LIST_HEAD(&memcg->mm_list.fifo);
++	spin_lock_init(&memcg->mm_list.lock);
++
+ 	for_each_node(nid) {
+ 		struct lruvec *lruvec = get_lruvec(nid, memcg);
+ 
+ 		lru_gen_init_state(memcg, lruvec);
+ 	}
+ }
++
++void lru_gen_free_memcg(struct mem_cgroup *memcg)
++{
++	int nid;
++
++	for_each_node(nid) {
++		int i;
++		struct lruvec *lruvec = get_lruvec(nid, memcg);
++
++		for (i = 0; i < NR_BLOOM_FILTERS; i++) {
++			bitmap_free(lruvec->mm_walk.filters[i]);
++			lruvec->mm_walk.filters[i] = NULL;
++		}
++	}
++}
+ #endif
+ 
+ static int __init init_lru_gen(void)
+ {
+ 	BUILD_BUG_ON(MIN_NR_GENS + 1 >= MAX_NR_GENS);
+ 	BUILD_BUG_ON(BIT(LRU_GEN_WIDTH) <= MAX_NR_GENS);
++	BUILD_BUG_ON(sizeof(MM_STAT_CODES) != NR_MM_STATS + 1);
+ 
+ 	return 0;
+ };

target/linux/generic/pending-5.15/020-05-mm-multigenerational-lru-aging.patch

@@ -0,0 +1,1176 @@
+From 8217cd2238c40cf77208aa27a7cc09879e685890 Mon Sep 17 00:00:00 2001
+From: Yu Zhao <[email protected]>
+Date: Mon, 5 Apr 2021 04:35:07 -0600
+Subject: [PATCH 06/10] mm: multigenerational lru: aging
+
+The aging produces young generations. Given an lruvec, the aging
+traverses lruvec_memcg()->mm_list and calls walk_page_range() to scan
+PTEs for accessed pages. Upon finding one, the aging updates its
+generation number to max_seq (modulo MAX_NR_GENS). After each round of
+traversal, the aging increments max_seq. The aging is due when
+min_seq[] reaches max_seq-1.
+
+The aging uses the following optimizations when walking page tables:
+  1) It skips non-leaf PMD entries that have the accessed bit cleared
+  when CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG=y.
+  2) It does not zigzag between a PGD table and the same PMD or PTE
+  table spanning multiple VMAs. In other words, it finishes all the
+  VMAs within the range of the same PMD or PTE table before it returns
+  to this PGD table. This optimizes workloads that have large numbers
+  of tiny VMAs, especially when CONFIG_PGTABLE_LEVELS=5.
+
+Signed-off-by: Yu Zhao <[email protected]>
+Tested-by: Konstantin Kharlamov <[email protected]>
+Change-Id: I3ae8abc3100d023cecb3a699d86020ae6fc10a45
+---
+ include/linux/memcontrol.h |   3 +
+ include/linux/mmzone.h     |   9 +
+ include/linux/oom.h        |  16 +
+ include/linux/swap.h       |   3 +
+ mm/memcontrol.c            |   5 +
+ mm/oom_kill.c              |   4 +-
+ mm/rmap.c                  |   8 +
+ mm/vmscan.c                | 948 +++++++++++++++++++++++++++++++++++++
+ 8 files changed, 994 insertions(+), 2 deletions(-)
+
+--- a/include/linux/memcontrol.h
++++ b/include/linux/memcontrol.h
+@@ -1367,10 +1367,13 @@ mem_cgroup_print_oom_meminfo(struct mem_
+ 
+ static inline void lock_page_memcg(struct page *page)
+ {
++	/* to match page_memcg_rcu() */
++	rcu_read_lock();
+ }
+ 
+ static inline void unlock_page_memcg(struct page *page)
+ {
++	rcu_read_unlock();
+ }
+ 
+ static inline void mem_cgroup_handle_over_high(void)
+--- a/include/linux/mmzone.h
++++ b/include/linux/mmzone.h
+@@ -295,6 +295,7 @@ enum lruvec_flags {
+ };
+ 
+ struct lruvec;
++struct page_vma_mapped_walk;
+ 
+ #define LRU_GEN_MASK		((BIT(LRU_GEN_WIDTH) - 1) << LRU_GEN_PGOFF)
+ #define LRU_REFS_MASK		((BIT(LRU_REFS_WIDTH) - 1) << LRU_REFS_PGOFF)
+@@ -393,6 +394,7 @@ struct mm_walk_args {
+ 
+ void lru_gen_init_state(struct mem_cgroup *memcg, struct lruvec *lruvec);
+ void lru_gen_change_state(bool enable, bool main, bool swap);
++void lru_gen_look_around(struct page_vma_mapped_walk *pvmw);
+ 
+ #ifdef CONFIG_MEMCG
+ void lru_gen_init_memcg(struct mem_cgroup *memcg);
+@@ -409,6 +411,10 @@ static inline void lru_gen_change_state(
+ {
+ }
+ 
++static inline void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
++{
++}
++
+ #ifdef CONFIG_MEMCG
+ static inline void lru_gen_init_memcg(struct mem_cgroup *memcg)
+ {
+@@ -1028,6 +1034,9 @@ typedef struct pglist_data {
+ 
+ 	unsigned long		flags;
+ 
++#ifdef CONFIG_LRU_GEN
++	struct mm_walk_args	mm_walk_args;
++#endif
+ 	ZONE_PADDING(_pad2_)
+ 
+ 	/* Per-node vmstats */
+--- a/include/linux/oom.h
++++ b/include/linux/oom.h
+@@ -57,6 +57,22 @@ struct oom_control {
+ extern struct mutex oom_lock;
+ extern struct mutex oom_adj_mutex;
+ 
++#ifdef CONFIG_MMU
++extern struct task_struct *oom_reaper_list;
++extern struct wait_queue_head oom_reaper_wait;
++
++static inline bool oom_reaping_in_progress(void)
++{
++	/* racy check to see if oom reaping could be in progress */
++	return READ_ONCE(oom_reaper_list) || !waitqueue_active(&oom_reaper_wait);
++}
++#else
++static inline bool oom_reaping_in_progress(void)
++{
++	return false;
++}
++#endif
++
+ static inline void set_current_oom_origin(void)
+ {
+ 	current->signal->oom_flag_origin = true;
+--- a/include/linux/swap.h
++++ b/include/linux/swap.h
+@@ -137,6 +137,9 @@ union swap_header {
+  */
+ struct reclaim_state {
+ 	unsigned long reclaimed_slab;
++#ifdef CONFIG_LRU_GEN
++	struct mm_walk_args *mm_walk_args;
++#endif
+ };
+ 
+ #ifdef __KERNEL__
+--- a/mm/memcontrol.c
++++ b/mm/memcontrol.c
+@@ -1304,12 +1304,17 @@ void mem_cgroup_update_lru_size(struct l
+ 		*lru_size += nr_pages;
+ 
+ 	size = *lru_size;
++#ifdef CONFIG_LRU_GEN
++	/* unlikely but not a bug when reset_batch_size() is pending */
++	VM_WARN_ON(size + MAX_BATCH_SIZE < 0);
++#else
+ 	if (WARN_ONCE(size < 0,
+ 		"%s(%p, %d, %d): lru_size %ld\n",
+ 		__func__, lruvec, lru, nr_pages, size)) {
+ 		VM_BUG_ON(1);
+ 		*lru_size = 0;
+ 	}
++#endif
+ 
+ 	if (nr_pages > 0)
+ 		*lru_size += nr_pages;
+--- a/mm/oom_kill.c
++++ b/mm/oom_kill.c
+@@ -508,8 +508,8 @@ bool process_shares_mm(struct task_struc
+  * victim (if that is possible) to help the OOM killer to move on.
+  */
+ static struct task_struct *oom_reaper_th;
+-static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
+-static struct task_struct *oom_reaper_list;
++DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
++struct task_struct *oom_reaper_list;
+ static DEFINE_SPINLOCK(oom_reaper_lock);
+ 
+ bool __oom_reap_task_mm(struct mm_struct *mm)
+--- a/mm/rmap.c
++++ b/mm/rmap.c
+@@ -73,6 +73,7 @@
+ #include <linux/page_idle.h>
+ #include <linux/memremap.h>
+ #include <linux/userfaultfd_k.h>
++#include <linux/mm_inline.h>
+ 
+ #include <asm/tlbflush.h>
+ 
+@@ -790,6 +791,13 @@ static bool page_referenced_one(struct p
+ 		}
+ 
+ 		if (pvmw.pte) {
++			/* the multigenerational lru exploits the spatial locality */
++			if (lru_gen_enabled() && pte_young(*pvmw.pte) &&
++			    !(vma->vm_flags & VM_SEQ_READ)) {
++				lru_gen_look_around(&pvmw);
++				referenced++;
++			}
++
+ 			if (ptep_clear_flush_young_notify(vma, address,
+ 						pvmw.pte)) {
+ 				/*
+--- a/mm/vmscan.c
++++ b/mm/vmscan.c
+@@ -51,6 +51,8 @@
+ #include <linux/dax.h>
+ #include <linux/psi.h>
+ #include <linux/memory.h>
++#include <linux/pagewalk.h>
++#include <linux/shmem_fs.h>
+ 
+ #include <asm/tlbflush.h>
+ #include <asm/div64.h>
+@@ -2887,6 +2889,15 @@ static bool can_age_anon_pages(struct pg
+  *                          shorthand helpers
+  ******************************************************************************/
+ 
++#define DEFINE_MAX_SEQ(lruvec)						\
++	unsigned long max_seq = READ_ONCE((lruvec)->evictable.max_seq)
++
++#define DEFINE_MIN_SEQ(lruvec)						\
++	unsigned long min_seq[ANON_AND_FILE] = {			\
++		READ_ONCE((lruvec)->evictable.min_seq[0]),		\
++		READ_ONCE((lruvec)->evictable.min_seq[1]),		\
++	}
++
+ #define for_each_gen_type_zone(gen, type, zone)				\
+ 	for ((gen) = 0; (gen) < MAX_NR_GENS; (gen)++)			\
+ 		for ((type) = 0; (type) < ANON_AND_FILE; (type)++)	\
+@@ -2899,6 +2910,12 @@ static int page_lru_gen(struct page *pag
+ 	return ((flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
+ }
+ 
++static int get_swappiness(struct mem_cgroup *memcg)
++{
++	return mem_cgroup_get_nr_swap_pages(memcg) >= MIN_BATCH_SIZE ?
++	       mem_cgroup_swappiness(memcg) : 0;
++}
++
+ static struct lruvec *get_lruvec(int nid, struct mem_cgroup *memcg)
+ {
+ 	struct pglist_data *pgdat = NODE_DATA(nid);
+@@ -3229,6 +3246,926 @@ done:
+ }
+ 
+ /******************************************************************************
++ *                          the aging
++ ******************************************************************************/
++
++static int page_update_gen(struct page *page, int gen)
++{
++	unsigned long old_flags, new_flags;
++
++	VM_BUG_ON(gen >= MAX_NR_GENS);
++
++	do {
++		new_flags = old_flags = READ_ONCE(page->flags);
++
++		if (!(new_flags & LRU_GEN_MASK)) {
++			new_flags |= BIT(PG_referenced);
++			continue;
++		}
++
++		new_flags &= ~LRU_GEN_MASK;
++		new_flags |= (gen + 1UL) << LRU_GEN_PGOFF;
++	} while (new_flags != old_flags &&
++		 cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
++
++	return ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
++}
++
++static void page_inc_gen(struct page *page, struct lruvec *lruvec, bool reclaiming)
++{
++	int old_gen, new_gen;
++	unsigned long old_flags, new_flags;
++	int type = page_is_file_lru(page);
++	int zone = page_zonenum(page);
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
++
++	do {
++		new_flags = old_flags = READ_ONCE(page->flags);
++		VM_BUG_ON_PAGE(!(new_flags & LRU_GEN_MASK), page);
++
++		new_gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
++		/* page_update_gen() has updated this page? */
++		if (new_gen >= 0 && new_gen != old_gen) {
++			list_move(&page->lru, &lrugen->lists[new_gen][type][zone]);
++			return;
++		}
++
++		new_gen = (old_gen + 1) % MAX_NR_GENS;
++
++		new_flags &= ~LRU_GEN_MASK;
++		new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF;
++		/* for end_page_writeback() */
++		if (reclaiming)
++			new_flags |= BIT(PG_reclaim);
++	} while (cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
++
++	lru_gen_update_size(page, lruvec, old_gen, new_gen);
++	if (reclaiming)
++		list_move(&page->lru, &lrugen->lists[new_gen][type][zone]);
++	else
++		list_move_tail(&page->lru, &lrugen->lists[new_gen][type][zone]);
++}
++
++static void update_batch_size(struct page *page, int old_gen, int new_gen,
++			      struct mm_walk_args *args)
++{
++	int type = page_is_file_lru(page);
++	int zone = page_zonenum(page);
++	int delta = thp_nr_pages(page);
++
++	VM_BUG_ON(old_gen >= MAX_NR_GENS);
++	VM_BUG_ON(new_gen >= MAX_NR_GENS);
++
++	args->batch_size++;
++
++	args->nr_pages[old_gen][type][zone] -= delta;
++	args->nr_pages[new_gen][type][zone] += delta;
++}
++
++static void reset_batch_size(struct lruvec *lruvec, struct mm_walk_args *args)
++{
++	int gen, type, zone;
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	args->batch_size = 0;
++
++	for_each_gen_type_zone(gen, type, zone) {
++		enum lru_list lru = type * LRU_FILE;
++		int delta = args->nr_pages[gen][type][zone];
++
++		if (!delta)
++			continue;
++
++		args->nr_pages[gen][type][zone] = 0;
++		WRITE_ONCE(lrugen->sizes[gen][type][zone],
++			   lrugen->sizes[gen][type][zone] + delta);
++
++		if (lru_gen_is_active(lruvec, gen))
++			lru += LRU_ACTIVE;
++		update_lru_size(lruvec, lru, zone, delta);
++	}
++}
++
++static int should_skip_vma(unsigned long start, unsigned long end, struct mm_walk *walk)
++{
++	struct address_space *mapping;
++	struct vm_area_struct *vma = walk->vma;
++	struct mm_walk_args *args = walk->private;
++
++	if (!vma_is_accessible(vma) || is_vm_hugetlb_page(vma) ||
++	    (vma->vm_flags & (VM_LOCKED | VM_SPECIAL | VM_SEQ_READ)))
++		return true;
++
++	if (vma_is_anonymous(vma))
++		return !args->swappiness;
++
++	if (WARN_ON_ONCE(!vma->vm_file || !vma->vm_file->f_mapping))
++		return true;
++
++	mapping = vma->vm_file->f_mapping;
++	if (!mapping->a_ops->writepage)
++		return true;
++
++	return (shmem_mapping(mapping) && !args->swappiness) || mapping_unevictable(mapping);
++}
++
++/*
++ * Some userspace memory allocators create many single-page VMAs. So instead of
++ * returning back to the PGD table for each of such VMAs, we finish at least an
++ * entire PMD table and therefore avoid many zigzags.
++ */
++static bool get_next_vma(struct mm_walk *walk, unsigned long mask, unsigned long size,
++			 unsigned long *start, unsigned long *end)
++{
++	unsigned long next = round_up(*end, size);
++
++	VM_BUG_ON(mask & size);
++	VM_BUG_ON(*start >= *end);
++	VM_BUG_ON((next & mask) != (*start & mask));
++
++	while (walk->vma) {
++		if (next >= walk->vma->vm_end) {
++			walk->vma = walk->vma->vm_next;
++			continue;
++		}
++
++		if ((next & mask) != (walk->vma->vm_start & mask))
++			return false;
++
++		if (should_skip_vma(walk->vma->vm_start, walk->vma->vm_end, walk)) {
++			walk->vma = walk->vma->vm_next;
++			continue;
++		}
++
++		*start = max(next, walk->vma->vm_start);
++		next = (next | ~mask) + 1;
++		/* rounded-up boundaries can wrap to 0 */
++		*end = next && next < walk->vma->vm_end ? next : walk->vma->vm_end;
++
++		return true;
++	}
++
++	return false;
++}
++
++static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
++			   struct mm_walk *walk)
++{
++	int i;
++	pte_t *pte;
++	spinlock_t *ptl;
++	unsigned long addr;
++	int worth = 0;
++	struct mm_walk_args *args = walk->private;
++	int old_gen, new_gen = lru_gen_from_seq(args->max_seq);
++
++	VM_BUG_ON(pmd_leaf(*pmd));
++
++	pte = pte_offset_map_lock(walk->mm, pmd, start & PMD_MASK, &ptl);
++	arch_enter_lazy_mmu_mode();
++restart:
++	for (i = pte_index(start), addr = start; addr != end; i++, addr += PAGE_SIZE) {
++		struct page *page;
++		unsigned long pfn = pte_pfn(pte[i]);
++
++		args->mm_stats[MM_LEAF_TOTAL]++;
++
++		if (!pte_present(pte[i]) || is_zero_pfn(pfn))
++			continue;
++
++		if (WARN_ON_ONCE(pte_devmap(pte[i]) || pte_special(pte[i])))
++			continue;
++
++		if (!pte_young(pte[i])) {
++			args->mm_stats[MM_LEAF_OLD]++;
++			continue;
++		}
++
++		VM_BUG_ON(!pfn_valid(pfn));
++		if (pfn < args->start_pfn || pfn >= args->end_pfn)
++			continue;
++
++		page = compound_head(pfn_to_page(pfn));
++		if (page_to_nid(page) != args->node_id)
++			continue;
++
++		if (page_memcg_rcu(page) != args->memcg)
++			continue;
++
++		VM_BUG_ON(addr < walk->vma->vm_start || addr >= walk->vma->vm_end);
++		if (!ptep_test_and_clear_young(walk->vma, addr, pte + i))
++			continue;
++
++		args->mm_stats[MM_LEAF_YOUNG]++;
++
++		if (pte_dirty(pte[i]) && !PageDirty(page) &&
++		    !(PageAnon(page) && PageSwapBacked(page) && !PageSwapCache(page)))
++			set_page_dirty(page);
++
++		old_gen = page_update_gen(page, new_gen);
++		if (old_gen >= 0 && old_gen != new_gen)
++			update_batch_size(page, old_gen, new_gen, args);
++
++		worth++;
++	}
++
++	if (i < PTRS_PER_PTE && get_next_vma(walk, PMD_MASK, PAGE_SIZE, &start, &end))
++		goto restart;
++
++	arch_leave_lazy_mmu_mode();
++	pte_unmap_unlock(pte, ptl);
++
++	return worth >= MIN_BATCH_SIZE / 2;
++}
++
++/*
++ * We scan PMD entries in two passes. The first pass reaches to PTE tables and
++ * doesn't take the PMD lock. The second pass clears the accessed bit on PMD
++ * entries and needs to take the PMD lock.
++ */
++#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG)
++static void walk_pmd_range_locked(pud_t *pud, unsigned long start, int offset,
++				  struct vm_area_struct *vma, struct mm_walk *walk)
++{
++	int i;
++	pmd_t *pmd;
++	spinlock_t *ptl;
++	struct mm_walk_args *args = walk->private;
++	int old_gen, new_gen = lru_gen_from_seq(args->max_seq);
++
++	VM_BUG_ON(pud_leaf(*pud));
++
++	start = (start & PUD_MASK) + offset * PMD_SIZE;
++	pmd = pmd_offset(pud, start);
++	ptl = pmd_lock(walk->mm, pmd);
++	arch_enter_lazy_mmu_mode();
++
++	for_each_set_bit(i, args->bitmap, MIN_BATCH_SIZE) {
++		struct page *page;
++		unsigned long pfn = pmd_pfn(pmd[i]);
++		unsigned long addr = start + i * PMD_SIZE;
++
++		if (!pmd_present(pmd[i]) || is_huge_zero_pmd(pmd[i]))
++			continue;
++
++		if (WARN_ON_ONCE(pmd_devmap(pmd[i])))
++			continue;
++
++		if (!pmd_trans_huge(pmd[i])) {
++			if (IS_ENABLED(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG))
++				pmdp_test_and_clear_young(vma, addr, pmd + i);
++			continue;
++		}
++
++		VM_BUG_ON(!pfn_valid(pfn));
++		if (pfn < args->start_pfn || pfn >= args->end_pfn)
++			continue;
++
++		page = pfn_to_page(pfn);
++		VM_BUG_ON_PAGE(PageTail(page), page);
++		if (page_to_nid(page) != args->node_id)
++			continue;
++
++		if (page_memcg_rcu(page) != args->memcg)
++			continue;
++
++		VM_BUG_ON(addr < vma->vm_start || addr >= vma->vm_end);
++		if (!pmdp_test_and_clear_young(vma, addr, pmd + i))
++			continue;
++
++		args->mm_stats[MM_LEAF_YOUNG]++;
++
++		if (pmd_dirty(pmd[i]) && !PageDirty(page) &&
++		    !(PageAnon(page) && PageSwapBacked(page) && !PageSwapCache(page)))
++			set_page_dirty(page);
++
++		old_gen = page_update_gen(page, new_gen);
++		if (old_gen >= 0 && old_gen != new_gen)
++			update_batch_size(page, old_gen, new_gen, args);
++	}
++
++	arch_leave_lazy_mmu_mode();
++	spin_unlock(ptl);
++
++	bitmap_zero(args->bitmap, MIN_BATCH_SIZE);
++}
++#else
++static void walk_pmd_range_locked(pud_t *pud, unsigned long start, int offset,
++				  struct vm_area_struct *vma, struct mm_walk *walk)
++{
++}
++#endif
++
++static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
++			   struct mm_walk *walk)
++{
++	int i;
++	pmd_t *pmd;
++	unsigned long next;
++	unsigned long addr;
++	struct vm_area_struct *vma;
++	int offset = -1;
++	bool reset = false;
++	struct mm_walk_args *args = walk->private;
++	struct lruvec *lruvec = get_lruvec(args->node_id, args->memcg);
++
++	VM_BUG_ON(pud_leaf(*pud));
++
++	pmd = pmd_offset(pud, start & PUD_MASK);
++restart:
++	vma = walk->vma;
++	for (i = pmd_index(start), addr = start; addr != end; i++, addr = next) {
++		pmd_t val = pmd_read_atomic(pmd + i);
++
++		/* for pmd_read_atomic() */
++		barrier();
++
++		next = pmd_addr_end(addr, end);
++
++		if (!pmd_present(val)) {
++			args->mm_stats[MM_LEAF_TOTAL]++;
++			continue;
++		}
++
++#ifdef CONFIG_TRANSPARENT_HUGEPAGE
++		if (pmd_trans_huge(val)) {
++			unsigned long pfn = pmd_pfn(val);
++
++			args->mm_stats[MM_LEAF_TOTAL]++;
++
++			if (is_huge_zero_pmd(val))
++				continue;
++
++			if (!pmd_young(val)) {
++				args->mm_stats[MM_LEAF_OLD]++;
++				continue;
++			}
++
++			if (pfn < args->start_pfn || pfn >= args->end_pfn)
++				continue;
++
++			if (offset < 0)
++				offset = i;
++			else if (i - offset >= MIN_BATCH_SIZE) {
++				walk_pmd_range_locked(pud, start, offset, vma, walk);
++				offset = i;
++			}
++			__set_bit(i - offset, args->bitmap);
++			reset = true;
++			continue;
++		}
++#endif
++		args->mm_stats[MM_NONLEAF_TOTAL]++;
++
++#ifdef CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG
++		if (!pmd_young(val))
++			continue;
++
++		if (offset < 0)
++			offset = i;
++		else if (i - offset >= MIN_BATCH_SIZE) {
++			walk_pmd_range_locked(pud, start, offset, vma, walk);
++			offset = i;
++			reset = false;
++		}
++		__set_bit(i - offset, args->bitmap);
++#endif
++		if (args->use_filter && !test_bloom_filter(lruvec, args->max_seq, pmd + i))
++			continue;
++
++		args->mm_stats[MM_NONLEAF_PREV]++;
++
++		if (!walk_pte_range(&val, addr, next, walk))
++			continue;
++
++		args->mm_stats[MM_NONLEAF_CUR]++;
++
++		set_bloom_filter(lruvec, args->max_seq + 1, pmd + i);
++	}
++
++	if (reset) {
++		walk_pmd_range_locked(pud, start, offset, vma, walk);
++		offset = -1;
++		reset = false;
++	}
++
++	if (i < PTRS_PER_PMD && get_next_vma(walk, PUD_MASK, PMD_SIZE, &start, &end))
++		goto restart;
++
++	if (offset >= 0)
++		walk_pmd_range_locked(pud, start, offset, vma, walk);
++}
++
++static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end,
++			  struct mm_walk *walk)
++{
++	int i;
++	pud_t *pud;
++	unsigned long addr;
++	unsigned long next;
++	struct mm_walk_args *args = walk->private;
++
++	VM_BUG_ON(p4d_leaf(*p4d));
++
++	pud = pud_offset(p4d, start & P4D_MASK);
++restart:
++	for (i = pud_index(start), addr = start; addr != end; i++, addr = next) {
++		pud_t val = READ_ONCE(pud[i]);
++
++		next = pud_addr_end(addr, end);
++
++		if (!pud_present(val) || WARN_ON_ONCE(pud_leaf(val)))
++			continue;
++
++		walk_pmd_range(&val, addr, next, walk);
++
++		if (args->batch_size >= MAX_BATCH_SIZE) {
++			end = (addr | ~PUD_MASK) + 1;
++			goto done;
++		}
++	}
++
++	if (i < PTRS_PER_PUD && get_next_vma(walk, P4D_MASK, PUD_SIZE, &start, &end))
++		goto restart;
++
++	end = round_up(end, P4D_SIZE);
++done:
++	/* rounded-up boundaries can wrap to 0 */
++	args->next_addr = end && walk->vma ? max(end, walk->vma->vm_start) : 0;
++
++	return -EAGAIN;
++}
++
++static void walk_mm(struct lruvec *lruvec, struct mm_struct *mm, struct mm_walk_args *args)
++{
++	static const struct mm_walk_ops mm_walk_ops = {
++		.test_walk = should_skip_vma,
++		.p4d_entry = walk_pud_range,
++	};
++
++	int err;
++
++	args->next_addr = FIRST_USER_ADDRESS;
++
++	do {
++		unsigned long start = args->next_addr;
++		unsigned long end = mm->highest_vm_end;
++
++		err = -EBUSY;
++
++		rcu_read_lock();
++#ifdef CONFIG_MEMCG
++		if (args->memcg && atomic_read(&args->memcg->moving_account))
++			goto contended;
++#endif
++		if (!mmap_read_trylock(mm))
++			goto contended;
++
++		err = walk_page_range(mm, start, end, &mm_walk_ops, args);
++
++		mmap_read_unlock(mm);
++
++		if (args->batch_size) {
++			spin_lock_irq(&lruvec->lru_lock);
++			reset_batch_size(lruvec, args);
++			spin_unlock_irq(&lruvec->lru_lock);
++		}
++contended:
++		rcu_read_unlock();
++
++		cond_resched();
++	} while (err == -EAGAIN && args->next_addr && !mm_is_oom_victim(mm));
++}
++
++static struct mm_walk_args *alloc_mm_walk_args(void)
++{
++	if (!current->reclaim_state || !current->reclaim_state->mm_walk_args)
++		return kvzalloc(sizeof(struct mm_walk_args), GFP_KERNEL);
++
++	return current->reclaim_state->mm_walk_args;
++}
++
++static void free_mm_walk_args(struct mm_walk_args *args)
++{
++	if (!current->reclaim_state || !current->reclaim_state->mm_walk_args)
++		kvfree(args);
++}
++
++static bool inc_min_seq(struct lruvec *lruvec, int type)
++{
++	int gen, zone;
++	int remaining = MAX_BATCH_SIZE;
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	VM_BUG_ON(!seq_is_valid(lruvec));
++
++	if (get_nr_gens(lruvec, type) != MAX_NR_GENS)
++		return true;
++
++	gen = lru_gen_from_seq(lrugen->min_seq[type]);
++
++	for (zone = 0; zone < MAX_NR_ZONES; zone++) {
++		struct list_head *head = &lrugen->lists[gen][type][zone];
++
++		while (!list_empty(head)) {
++			struct page *page = lru_to_page(head);
++
++			VM_BUG_ON_PAGE(PageTail(page), page);
++			VM_BUG_ON_PAGE(PageUnevictable(page), page);
++			VM_BUG_ON_PAGE(PageActive(page), page);
++			VM_BUG_ON_PAGE(page_is_file_lru(page) != type, page);
++			VM_BUG_ON_PAGE(page_zonenum(page) != zone, page);
++
++			prefetchw_prev_lru_page(page, head, flags);
++
++			page_inc_gen(page, lruvec, false);
++
++			if (!--remaining)
++				return false;
++		}
++	}
++
++	WRITE_ONCE(lrugen->min_seq[type], lrugen->min_seq[type] + 1);
++
++	return true;
++}
++
++static bool try_to_inc_min_seq(struct lruvec *lruvec, int swappiness)
++{
++	int gen, type, zone;
++	bool success = false;
++	struct lrugen *lrugen = &lruvec->evictable;
++	DEFINE_MIN_SEQ(lruvec);
++
++	VM_BUG_ON(!seq_is_valid(lruvec));
++
++	for (type = 0; type < ANON_AND_FILE; type++) {
++		while (lrugen->max_seq - min_seq[type] >= MIN_NR_GENS) {
++			gen = lru_gen_from_seq(min_seq[type]);
++
++			for (zone = 0; zone < MAX_NR_ZONES; zone++) {
++				if (!list_empty(&lrugen->lists[gen][type][zone]))
++					goto next;
++			}
++
++			min_seq[type]++;
++		}
++next:
++		;
++	}
++
++	min_seq[0] = min(min_seq[0], min_seq[1]);
++	if (swappiness)
++		min_seq[1] = max(min_seq[0], lrugen->min_seq[1]);
++
++	for (type = 0; type < ANON_AND_FILE; type++) {
++		if (min_seq[type] == lrugen->min_seq[type])
++			continue;
++
++		WRITE_ONCE(lrugen->min_seq[type], min_seq[type]);
++		success = true;
++	}
++
++	return success;
++}
++
++static void inc_max_seq(struct lruvec *lruvec, unsigned long max_seq)
++{
++	int gen, type, zone;
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	spin_lock_irq(&lruvec->lru_lock);
++
++	VM_BUG_ON(!seq_is_valid(lruvec));
++
++	if (max_seq != lrugen->max_seq)
++		goto unlock;
++
++	if (!try_to_inc_min_seq(lruvec, true)) {
++		for (type = ANON_AND_FILE - 1; type >= 0; type--) {
++			while (!inc_min_seq(lruvec, type)) {
++				spin_unlock_irq(&lruvec->lru_lock);
++				cond_resched();
++				spin_lock_irq(&lruvec->lru_lock);
++			}
++		}
++	}
++
++	gen = lru_gen_from_seq(lrugen->max_seq - 1);
++	for (type = 0; type < ANON_AND_FILE; type++) {
++		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
++			enum lru_list lru = type * LRU_FILE;
++			long delta = lrugen->sizes[gen][type][zone];
++
++			if (!delta)
++				continue;
++
++			WARN_ON_ONCE(delta != (int)delta);
++
++			update_lru_size(lruvec, lru, zone, delta);
++			update_lru_size(lruvec, lru + LRU_ACTIVE, zone, -delta);
++		}
++	}
++
++	gen = lru_gen_from_seq(lrugen->max_seq + 1);
++	for (type = 0; type < ANON_AND_FILE; type++) {
++		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
++			enum lru_list lru = type * LRU_FILE;
++			long delta = lrugen->sizes[gen][type][zone];
++
++			if (!delta)
++				continue;
++
++			WARN_ON_ONCE(delta != (int)delta);
++
++			update_lru_size(lruvec, lru, zone, -delta);
++			update_lru_size(lruvec, lru + LRU_ACTIVE, zone, delta);
++		}
++	}
++
++	WRITE_ONCE(lrugen->timestamps[gen], jiffies);
++	/* make sure all preceding modifications appear first */
++	smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1);
++unlock:
++	spin_unlock_irq(&lruvec->lru_lock);
++}
++
++/* Main function used by the foreground, the background and the user-triggered aging. */
++static bool try_to_inc_max_seq(struct lruvec *lruvec, struct scan_control *sc, int swappiness,
++			       unsigned long max_seq, bool use_filter)
++{
++	bool last;
++	struct mm_walk_args *args;
++	struct mm_struct *mm = NULL;
++	struct lrugen *lrugen = &lruvec->evictable;
++	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
++	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
++	int nid = pgdat->node_id;
++
++	VM_BUG_ON(max_seq > READ_ONCE(lrugen->max_seq));
++
++	/*
++	 * If we are not from run_aging() and clearing the accessed bit may
++	 * trigger page faults, then don't proceed to clearing all accessed
++	 * PTEs. Instead, fallback to lru_gen_look_around(), which only clears a
++	 * handful of accessed PTEs. This is less efficient but causes fewer
++	 * page faults on CPUs that don't have the capability.
++	 */
++	if ((current->flags & PF_MEMALLOC) && !arch_has_hw_pte_young(false)) {
++		inc_max_seq(lruvec, max_seq);
++		return true;
++	}
++
++	args = alloc_mm_walk_args();
++	if (!args)
++		return false;
++
++	args->memcg = memcg;
++	args->max_seq = max_seq;
++	args->start_pfn = pgdat->node_start_pfn;
++	args->end_pfn = pgdat_end_pfn(pgdat);
++	args->node_id = nid;
++	args->swappiness = swappiness;
++	args->use_filter = use_filter;
++
++	do {
++		last = get_next_mm(lruvec, args, &mm);
++		if (mm)
++			walk_mm(lruvec, mm, args);
++
++		cond_resched();
++	} while (mm);
++
++	free_mm_walk_args(args);
++
++	if (!last) {
++		/* don't wait unless we may have trouble reclaiming */
++		if (!current_is_kswapd() && sc->priority < DEF_PRIORITY - 2)
++			wait_event_killable(lruvec->mm_walk.wait,
++					    max_seq < READ_ONCE(lrugen->max_seq));
++
++		return max_seq < READ_ONCE(lrugen->max_seq);
++	}
++
++	VM_BUG_ON(max_seq != READ_ONCE(lrugen->max_seq));
++
++	inc_max_seq(lruvec, max_seq);
++	/* either we see any waiters or they will see updated max_seq */
++	if (wq_has_sleeper(&lruvec->mm_walk.wait))
++		wake_up_all(&lruvec->mm_walk.wait);
++
++	wakeup_flusher_threads(WB_REASON_VMSCAN);
++
++	return true;
++}
++
++static long get_nr_evictable(struct lruvec *lruvec, struct scan_control *sc, int swappiness,
++			     unsigned long max_seq, unsigned long *min_seq, bool *low)
++{
++	int gen, type, zone;
++	long max = 0;
++	long min = 0;
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	for (type = !swappiness; type < ANON_AND_FILE; type++) {
++		unsigned long seq;
++
++		for (seq = min_seq[type]; seq <= max_seq; seq++) {
++			long size = 0;
++
++			gen = lru_gen_from_seq(seq);
++
++			for (zone = 0; zone <= sc->reclaim_idx; zone++)
++				size += READ_ONCE(lrugen->sizes[gen][type][zone]);
++
++			max += size;
++			if (type && max_seq - seq >= MIN_NR_GENS)
++				min += size;
++		}
++	}
++
++	*low = max_seq - min_seq[1] <= MIN_NR_GENS && min < MIN_BATCH_SIZE;
++
++	return max > 0 ? max : 0;
++}
++
++static bool age_lruvec(struct lruvec *lruvec, struct scan_control *sc,
++		       unsigned long min_ttl)
++{
++	bool low;
++	long nr_to_scan;
++	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
++	int swappiness = get_swappiness(memcg);
++	DEFINE_MAX_SEQ(lruvec);
++	DEFINE_MIN_SEQ(lruvec);
++
++	if (mem_cgroup_below_min(memcg))
++		return false;
++
++	if (min_ttl) {
++		int gen = lru_gen_from_seq(min_seq[1]);
++		unsigned long birth = READ_ONCE(lruvec->evictable.timestamps[gen]);
++
++		if (time_is_after_jiffies(birth + min_ttl))
++			return false;
++	}
++
++	nr_to_scan = get_nr_evictable(lruvec, sc, swappiness, max_seq, min_seq, &low);
++	if (!nr_to_scan)
++		return false;
++
++	nr_to_scan >>= sc->priority;
++
++	if (!mem_cgroup_online(memcg))
++		nr_to_scan++;
++
++	if (nr_to_scan && low && (!mem_cgroup_below_low(memcg) || sc->memcg_low_reclaim))
++		try_to_inc_max_seq(lruvec, sc, swappiness, max_seq, true);
++
++	return true;
++}
++
++/* Protect the working set accessed within the last N milliseconds. */
++static unsigned long lru_gen_min_ttl __read_mostly;
++
++static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
++{
++	struct mem_cgroup *memcg;
++	bool success = false;
++	unsigned long min_ttl = READ_ONCE(lru_gen_min_ttl);
++
++	VM_BUG_ON(!current_is_kswapd());
++
++	if (!sc->force_deactivate) {
++		sc->force_deactivate = 1;
++		return;
++	}
++
++	current->reclaim_state->mm_walk_args = &pgdat->mm_walk_args;
++
++	memcg = mem_cgroup_iter(NULL, NULL, NULL);
++	do {
++		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
++
++		if (age_lruvec(lruvec, sc, min_ttl))
++			success = true;
++
++		cond_resched();
++	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
++
++	if (!success && mutex_trylock(&oom_lock)) {
++		struct oom_control oc = {
++			.gfp_mask = sc->gfp_mask,
++			.order = sc->order,
++		};
++
++		/* to avoid overkilling */
++		if (!oom_reaping_in_progress())
++			out_of_memory(&oc);
++
++		mutex_unlock(&oom_lock);
++	}
++
++	current->reclaim_state->mm_walk_args = NULL;
++}
++
++/* Scan the vicinity of an accessed PTE when shrink_page_list() uses the rmap. */
++void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
++{
++	int i;
++	pte_t *pte;
++	struct page *page;
++	int old_gen, new_gen;
++	unsigned long start;
++	unsigned long end;
++	unsigned long addr;
++	struct mm_walk_args *args;
++	int worth = 0;
++	struct mem_cgroup *memcg = page_memcg(pvmw->page);
++	struct pglist_data *pgdat = page_pgdat(pvmw->page);
++	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
++	DEFINE_MAX_SEQ(lruvec);
++
++	lockdep_assert_held(pvmw->ptl);
++	VM_BUG_ON_PAGE(PageLRU(pvmw->page), pvmw->page);
++
++	args = current->reclaim_state ? current->reclaim_state->mm_walk_args : NULL;
++	if (!args)
++		return;
++
++	start = max(pvmw->address & PMD_MASK, pvmw->vma->vm_start);
++	end = min(pvmw->address | ~PMD_MASK, pvmw->vma->vm_end - 1) + 1;
++
++	if (end - start > MIN_BATCH_SIZE * PAGE_SIZE) {
++		if (pvmw->address - start < MIN_BATCH_SIZE * PAGE_SIZE / 2)
++			end = start + MIN_BATCH_SIZE * PAGE_SIZE;
++		else if (end - pvmw->address < MIN_BATCH_SIZE * PAGE_SIZE / 2)
++			start = end - MIN_BATCH_SIZE * PAGE_SIZE;
++		else {
++			start = pvmw->address - MIN_BATCH_SIZE * PAGE_SIZE / 2;
++			end = pvmw->address + MIN_BATCH_SIZE * PAGE_SIZE / 2;
++		}
++	}
++
++	pte = pvmw->pte - (pvmw->address - start) / PAGE_SIZE;
++	new_gen = lru_gen_from_seq(max_seq);
++
++	lock_page_memcg(pvmw->page);
++	arch_enter_lazy_mmu_mode();
++
++	for (i = 0, addr = start; addr != end; i++, addr += PAGE_SIZE) {
++		unsigned long pfn = pte_pfn(pte[i]);
++
++		if (!pte_present(pte[i]) || is_zero_pfn(pfn))
++			continue;
++
++		if (WARN_ON_ONCE(pte_devmap(pte[i]) || pte_special(pte[i])))
++			continue;
++
++		VM_BUG_ON(!pfn_valid(pfn));
++		if (pfn < pgdat->node_start_pfn || pfn >= pgdat_end_pfn(pgdat))
++			continue;
++
++		worth++;
++
++		if (!pte_young(pte[i]))
++			continue;
++
++		page = compound_head(pfn_to_page(pfn));
++		if (page_to_nid(page) != pgdat->node_id)
++			continue;
++
++		if (page_memcg_rcu(page) != memcg)
++			continue;
++
++		VM_BUG_ON(addr < pvmw->vma->vm_start || addr >= pvmw->vma->vm_end);
++		if (!ptep_test_and_clear_young(pvmw->vma, addr, pte + i))
++			continue;
++
++		if (pte_dirty(pte[i]) && !PageDirty(page) &&
++		    !(PageAnon(page) && PageSwapBacked(page) && !PageSwapCache(page)))
++			__set_bit(i, args->bitmap);
++
++		old_gen = page_update_gen(page, new_gen);
++		if (old_gen >= 0 && old_gen != new_gen)
++			update_batch_size(page, old_gen, new_gen, args);
++	}
++
++	arch_leave_lazy_mmu_mode();
++	unlock_page_memcg(pvmw->page);
++
++	if (worth >= MIN_BATCH_SIZE / 2)
++		set_bloom_filter(lruvec, max_seq, pvmw->pmd);
++
++	for_each_set_bit(i, args->bitmap, MIN_BATCH_SIZE)
++		set_page_dirty(pte_page(pte[i]));
++
++	bitmap_zero(args->bitmap, MIN_BATCH_SIZE);
++}
++
++/******************************************************************************
+  *                          state change
+  ******************************************************************************/
+ 
+@@ -3477,6 +4414,12 @@ static int __init init_lru_gen(void)
+ };
+ late_initcall(init_lru_gen);
+ 
++#else
++
++static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
++{
++}
++
+ #endif /* CONFIG_LRU_GEN */
+ 
+ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
+@@ -4333,6 +5276,11 @@ static void age_active_anon(struct pglis
+ 	struct mem_cgroup *memcg;
+ 	struct lruvec *lruvec;
+ 
++	if (lru_gen_enabled()) {
++		lru_gen_age_node(pgdat, sc);
++		return;
++	}
++
+ 	if (!can_age_anon_pages(pgdat, sc))
+ 		return;
+ 

target/linux/generic/pending-5.15/020-06-mm-multigenerational-lru-eviction.patch

@@ -0,0 +1,1002 @@
+From f4b881ce07ccb2a519f664afaa2a68225b612ca3 Mon Sep 17 00:00:00 2001
+From: Yu Zhao <[email protected]>
+Date: Tue, 29 Jun 2021 20:46:47 -0600
+Subject: [PATCH 07/10] mm: multigenerational lru: eviction
+
+The eviction consumes old generations. Given an lruvec, the eviction
+scans pages on lrugen->lists indexed by anon and file min_seq[]
+(modulo MAX_NR_GENS). It first tries to select a type based on the
+values of min_seq[]. If they are equal, it selects the type that has
+a lower refaulted %. The eviction sorts a page according to its
+updated generation number if the aging has found this page accessed.
+It also moves a page to the next generation if this page is from an
+upper tier that has a higher refaulted % than the base tier. The
+eviction increments min_seq[] of a selected type when it finds
+lrugen->lists indexed by min_seq[] of this selected type are empty.
+
+Each generation is divided into multiple tiers. Tiers represent
+different ranges of numbers of accesses from file descriptors only.
+Pages accessed N times via file descriptors belong to tier
+order_base_2(N). Each generation contains at most MAX_NR_TIERS tiers,
+and they require additional MAX_NR_TIERS-2 bits in page->flags. In
+contrast to moving between generations which requires list operations,
+moving between tiers only involves operations on page->flags and
+therefore has a negligible cost. A feedback loop modeled after the PID
+controller monitors refaulted % across all tiers and decides when to
+protect pages from which tiers.
+
+Unmapped pages are initially added to the oldest generation and then
+conditionally protected by tiers. Each tier keeps track of how many
+pages from it have refaulted. Tier 0 is the base tier and pages from
+it are evicted unconditionally because there are no better candidates.
+Pages from an upper tier are either evicted or moved to the next
+generation, depending on whether this upper tier has a higher
+refaulted % than the base tier. This model has the following
+advantages:
+  1) It removes the cost in the buffered access path and reduces the
+  overall cost of protection because pages are conditionally protected
+  in the reclaim path.
+  2) It takes mapped pages into account and avoids overprotecting
+  pages accessed multiple times via file descriptors.
+  3 Additional tiers improve the protection of pages accessed more
+  than twice.
+
+Signed-off-by: Yu Zhao <[email protected]>
+Tested-by: Konstantin Kharlamov <[email protected]>
+Change-Id: I64c06d8f2cdb83ac7d56c7e1d07f043483956cac
+---
+ include/linux/mm_inline.h |  10 +
+ include/linux/mmzone.h    |  33 +++
+ mm/swap.c                 |  42 +++
+ mm/vmscan.c               | 555 +++++++++++++++++++++++++++++++++++++-
+ mm/workingset.c           | 120 ++++++++-
+ 5 files changed, 757 insertions(+), 3 deletions(-)
+
+--- a/include/linux/mm_inline.h
++++ b/include/linux/mm_inline.h
+@@ -106,6 +106,14 @@ static inline int lru_hist_from_seq(unsi
+ 	return seq % NR_HIST_GENS;
+ }
+ 
++/* Convert the number of accesses to a tier. See the comment on MAX_NR_TIERS. */
++static inline int lru_tier_from_refs(int refs)
++{
++	VM_BUG_ON(refs > BIT(LRU_REFS_WIDTH));
++
++	return order_base_2(refs + 1);
++}
++
+ /* The youngest and the second youngest generations are counted as active. */
+ static inline bool lru_gen_is_active(struct lruvec *lruvec, int gen)
+ {
+@@ -226,6 +234,8 @@ static inline bool lru_gen_del_page(stru
+ 		gen = ((new_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
+ 
+ 		new_flags &= ~LRU_GEN_MASK;
++		if ((new_flags & LRU_REFS_FLAGS) != LRU_REFS_FLAGS)
++			new_flags &= ~(LRU_REFS_MASK | LRU_REFS_FLAGS);
+ 		/* for shrink_page_list() */
+ 		if (reclaiming)
+ 			new_flags &= ~(BIT(PG_referenced) | BIT(PG_reclaim));
+--- a/include/linux/mmzone.h
++++ b/include/linux/mmzone.h
+@@ -319,6 +319,30 @@ struct page_vma_mapped_walk;
+ #define MIN_NR_GENS		2
+ #define MAX_NR_GENS		((unsigned int)CONFIG_NR_LRU_GENS)
+ 
++/*
++ * Each generation is divided into multiple tiers. Tiers represent different
++ * ranges of numbers of accesses from file descriptors, i.e.,
++ * mark_page_accessed(). In contrast to moving between generations which
++ * requires the lru lock, moving between tiers only involves an atomic
++ * operation on page->flags and therefore has a negligible cost.
++ *
++ * The purposes of tiers are to:
++ *   1) estimate whether pages accessed multiple times via file descriptors are
++ *   more active than pages accessed only via page tables by separating the two
++ *   access types into upper tiers and the base tier, and comparing refaulted %
++ *   across all tiers.
++ *   2) improve buffered io performance by deferring the protection of pages
++ *   accessed multiple times until the eviction. That is the protection happens
++ *   in the reclaim path, not the access path.
++ *
++ * Pages accessed N times via file descriptors belong to tier order_base_2(N).
++ * The base tier may be marked by PageReferenced(). All upper tiers are marked
++ * by PageReferenced() && PageWorkingset(). Additional bits from page->flags are
++ * used to support more than one upper tier.
++ */
++#define MAX_NR_TIERS		((unsigned int)CONFIG_TIERS_PER_GEN)
++#define LRU_REFS_FLAGS		(BIT(PG_referenced) | BIT(PG_workingset))
++
+ /* Whether to keep stats for historical generations. */
+ #ifdef CONFIG_LRU_GEN_STATS
+ #define NR_HIST_GENS		((unsigned int)CONFIG_NR_LRU_GENS)
+@@ -337,6 +361,15 @@ struct lrugen {
+ 	struct list_head lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
+ 	/* the sizes of the multigenerational lru lists in pages */
+ 	unsigned long sizes[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
++	/* the exponential moving average of refaulted */
++	unsigned long avg_refaulted[ANON_AND_FILE][MAX_NR_TIERS];
++	/* the exponential moving average of protected+evicted */
++	unsigned long avg_total[ANON_AND_FILE][MAX_NR_TIERS];
++	/* the base tier isn't protected, hence the minus one */
++	unsigned long protected[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS - 1];
++	/* incremented without holding the lru lock */
++	atomic_long_t evicted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS];
++	atomic_long_t refaulted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS];
+ 	/* whether the multigenerational lru is enabled */
+ 	bool enabled[ANON_AND_FILE];
+ };
+--- a/mm/swap.c
++++ b/mm/swap.c
+@@ -389,6 +389,43 @@ static void __lru_cache_activate_page(st
+ 	local_unlock(&lru_pvecs.lock);
+ }
+ 
++#ifdef CONFIG_LRU_GEN
++static void page_inc_refs(struct page *page)
++{
++	unsigned long refs;
++	unsigned long old_flags, new_flags;
++
++	if (PageUnevictable(page))
++		return;
++
++	/* see the comment on MAX_NR_TIERS */
++	do {
++		new_flags = old_flags = READ_ONCE(page->flags);
++
++		if (!(new_flags & BIT(PG_referenced))) {
++			new_flags |= BIT(PG_referenced);
++			continue;
++		}
++
++		if (!(new_flags & BIT(PG_workingset))) {
++			new_flags |= BIT(PG_workingset);
++			continue;
++		}
++
++		refs = new_flags & LRU_REFS_MASK;
++		refs = min(refs + BIT(LRU_REFS_PGOFF), LRU_REFS_MASK);
++
++		new_flags &= ~LRU_REFS_MASK;
++		new_flags |= refs;
++	} while (new_flags != old_flags &&
++		 cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
++}
++#else
++static void page_inc_refs(struct page *page)
++{
++}
++#endif /* CONFIG_LRU_GEN */
++
+ /*
+  * Mark a page as having seen activity.
+  *
+@@ -403,6 +440,11 @@ void mark_page_accessed(struct page *pag
+ {
+ 	page = compound_head(page);
+ 
++	if (lru_gen_enabled()) {
++		page_inc_refs(page);
++		return;
++	}
++
+ 	if (!PageReferenced(page)) {
+ 		SetPageReferenced(page);
+ 	} else if (PageUnevictable(page)) {
+--- a/mm/vmscan.c
++++ b/mm/vmscan.c
+@@ -1145,9 +1145,11 @@ static int __remove_mapping(struct addre
+ 
+ 	if (PageSwapCache(page)) {
+ 		swp_entry_t swap = { .val = page_private(page) };
+-		mem_cgroup_swapout(page, swap);
++
++		/* get a shadow entry before page_memcg() is cleared */
+ 		if (reclaimed && !mapping_exiting(mapping))
+ 			shadow = workingset_eviction(page, target_memcg);
++		mem_cgroup_swapout(page, swap);
+ 		__delete_from_swap_cache(page, swap, shadow);
+ 		xa_unlock_irq(&mapping->i_pages);
+ 		put_swap_page(page, swap);
+@@ -1410,6 +1412,11 @@ retry:
+ 		if (!sc->may_unmap && page_mapped(page))
+ 			goto keep_locked;
+ 
++		/* lru_gen_look_around() has updated this page? */
++		if (lru_gen_enabled() && !ignore_references &&
++		    page_mapped(page) && PageReferenced(page))
++			goto keep_locked;
++
+ 		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
+ 			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
+ 
+@@ -2570,6 +2577,9 @@ static void prepare_scan_count(pg_data_t
+ 	unsigned long file;
+ 	struct lruvec *target_lruvec;
+ 
++	if (lru_gen_enabled())
++		return;
++
+ 	target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);
+ 
+ 	/*
+@@ -2910,6 +2920,17 @@ static int page_lru_gen(struct page *pag
+ 	return ((flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
+ }
+ 
++static int page_lru_tier(struct page *page)
++{
++	int refs;
++	unsigned long flags = READ_ONCE(page->flags);
++
++	refs = (flags & LRU_REFS_FLAGS) == LRU_REFS_FLAGS ?
++	       ((flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF) + 1 : 0;
++
++	return lru_tier_from_refs(refs);
++}
++
+ static int get_swappiness(struct mem_cgroup *memcg)
+ {
+ 	return mem_cgroup_get_nr_swap_pages(memcg) >= MIN_BATCH_SIZE ?
+@@ -3246,6 +3267,91 @@ done:
+ }
+ 
+ /******************************************************************************
++ *                          refault feedback loop
++ ******************************************************************************/
++
++/*
++ * A feedback loop modeled after the PID controller. Currently supports the
++ * proportional (P) and the integral (I) terms; the derivative (D) term can be
++ * added if necessary. The setpoint (SP) is the desired position; the process
++ * variable (PV) is the measured position. The error is the difference between
++ * the SP and the PV. A positive error results in a positive control output
++ * correction, which, in our case, is to allow eviction.
++ *
++ * The P term is refaulted % of the current generation being evicted. The I
++ * term is the exponential moving average of refaulted % of previously evicted
++ * generations, using the smoothing factor 1/2.
++ *
++ * Our goal is to maintain proportional refaulted % across all tiers.
++ */
++struct ctrl_pos {
++	unsigned long refaulted;
++	unsigned long total;
++	int gain;
++};
++
++static void read_ctrl_pos(struct lruvec *lruvec, int type, int tier, int gain,
++			  struct ctrl_pos *pos)
++{
++	struct lrugen *lrugen = &lruvec->evictable;
++	int hist = lru_hist_from_seq(lrugen->min_seq[type]);
++
++	pos->refaulted = lrugen->avg_refaulted[type][tier] +
++			 atomic_long_read(&lrugen->refaulted[hist][type][tier]);
++	pos->total = lrugen->avg_total[type][tier] +
++		     atomic_long_read(&lrugen->evicted[hist][type][tier]);
++	if (tier)
++		pos->total += lrugen->protected[hist][type][tier - 1];
++	pos->gain = gain;
++}
++
++static void reset_ctrl_pos(struct lruvec *lruvec, int gen, int type)
++{
++	int tier;
++	int hist = lru_hist_from_seq(gen);
++	struct lrugen *lrugen = &lruvec->evictable;
++	bool carryover = gen == lru_gen_from_seq(lrugen->min_seq[type]);
++	bool clear = carryover ? NR_HIST_GENS == 1 : NR_HIST_GENS > 1;
++
++	if (!carryover && !clear)
++		return;
++
++	for (tier = 0; tier < MAX_NR_TIERS; tier++) {
++		if (carryover) {
++			unsigned long sum;
++
++			sum = lrugen->avg_refaulted[type][tier] +
++			      atomic_long_read(&lrugen->refaulted[hist][type][tier]);
++			WRITE_ONCE(lrugen->avg_refaulted[type][tier], sum / 2);
++
++			sum = lrugen->avg_total[type][tier] +
++			      atomic_long_read(&lrugen->evicted[hist][type][tier]);
++			if (tier)
++				sum += lrugen->protected[hist][type][tier - 1];
++			WRITE_ONCE(lrugen->avg_total[type][tier], sum / 2);
++		}
++
++		if (clear) {
++			atomic_long_set(&lrugen->refaulted[hist][type][tier], 0);
++			atomic_long_set(&lrugen->evicted[hist][type][tier], 0);
++			if (tier)
++				WRITE_ONCE(lrugen->protected[hist][type][tier - 1], 0);
++		}
++	}
++}
++
++static bool positive_ctrl_err(struct ctrl_pos *sp, struct ctrl_pos *pv)
++{
++	/*
++	 * Allow eviction if the PV has a limited number of refaulted pages or a
++	 * lower refaulted % than the SP.
++	 */
++	return pv->refaulted < MIN_BATCH_SIZE ||
++	       pv->refaulted * max(sp->total, 1UL) * sp->gain <=
++	       sp->refaulted * max(pv->total, 1UL) * pv->gain;
++}
++
++/******************************************************************************
+  *                          the aging
+  ******************************************************************************/
+ 
+@@ -3265,6 +3371,7 @@ static int page_update_gen(struct page *
+ 
+ 		new_flags &= ~LRU_GEN_MASK;
+ 		new_flags |= (gen + 1UL) << LRU_GEN_PGOFF;
++		new_flags &= ~(LRU_REFS_MASK | LRU_REFS_FLAGS);
+ 	} while (new_flags != old_flags &&
+ 		 cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
+ 
+@@ -3296,6 +3403,7 @@ static void page_inc_gen(struct page *pa
+ 
+ 		new_flags &= ~LRU_GEN_MASK;
+ 		new_flags |= (new_gen + 1UL) << LRU_GEN_PGOFF;
++		new_flags &= ~(LRU_REFS_MASK | LRU_REFS_FLAGS);
+ 		/* for end_page_writeback() */
+ 		if (reclaiming)
+ 			new_flags |= BIT(PG_reclaim);
+@@ -3787,6 +3895,7 @@ static bool inc_min_seq(struct lruvec *l
+ 		}
+ 	}
+ 
++	reset_ctrl_pos(lruvec, gen, type);
+ 	WRITE_ONCE(lrugen->min_seq[type], lrugen->min_seq[type] + 1);
+ 
+ 	return true;
+@@ -3824,6 +3933,8 @@ next:
+ 		if (min_seq[type] == lrugen->min_seq[type])
+ 			continue;
+ 
++		gen = lru_gen_from_seq(lrugen->min_seq[type]);
++		reset_ctrl_pos(lruvec, gen, type);
+ 		WRITE_ONCE(lrugen->min_seq[type], min_seq[type]);
+ 		success = true;
+ 	}
+@@ -3885,6 +3996,9 @@ static void inc_max_seq(struct lruvec *l
+ 		}
+ 	}
+ 
++	for (type = 0; type < ANON_AND_FILE; type++)
++		reset_ctrl_pos(lruvec, gen, type);
++
+ 	WRITE_ONCE(lrugen->timestamps[gen], jiffies);
+ 	/* make sure all preceding modifications appear first */
+ 	smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1);
+@@ -4166,6 +4280,433 @@ void lru_gen_look_around(struct page_vma
+ }
+ 
+ /******************************************************************************
++ *                          the eviction
++ ******************************************************************************/
++
++static bool sort_page(struct page *page, struct lruvec *lruvec, int tier_idx)
++{
++	bool success;
++	int gen = page_lru_gen(page);
++	int type = page_is_file_lru(page);
++	int zone = page_zonenum(page);
++	int tier = page_lru_tier(page);
++	int delta = thp_nr_pages(page);
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	VM_BUG_ON_PAGE(gen >= MAX_NR_GENS, page);
++
++	/* an mlocked page? */
++	if (!page_evictable(page)) {
++		success = lru_gen_del_page(page, lruvec, true);
++		VM_BUG_ON_PAGE(!success, page);
++		SetPageUnevictable(page);
++		add_page_to_lru_list(page, lruvec);
++		__count_vm_events(UNEVICTABLE_PGCULLED, delta);
++		return true;
++	}
++
++	/* a lazy-free page that has been written into? */
++	if (type && PageDirty(page) && PageAnon(page)) {
++		success = lru_gen_del_page(page, lruvec, true);
++		VM_BUG_ON_PAGE(!success, page);
++		SetPageSwapBacked(page);
++		add_page_to_lru_list_tail(page, lruvec);
++		return true;
++	}
++
++	/* page_update_gen() has updated this page? */
++	if (gen != lru_gen_from_seq(lrugen->min_seq[type])) {
++		list_move(&page->lru, &lrugen->lists[gen][type][zone]);
++		return true;
++	}
++
++	/* protect this page if its tier has a higher refaulted % */
++	if (tier > tier_idx) {
++		int hist = lru_hist_from_seq(gen);
++
++		page_inc_gen(page, lruvec, false);
++		WRITE_ONCE(lrugen->protected[hist][type][tier - 1],
++			   lrugen->protected[hist][type][tier - 1] + delta);
++		__mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta);
++		return true;
++	}
++
++	/* mark this page for reclaim if it's pending writeback */
++	if (PageWriteback(page) || (type && PageDirty(page))) {
++		page_inc_gen(page, lruvec, true);
++		return true;
++	}
++
++	return false;
++}
++
++static bool isolate_page(struct page *page, struct lruvec *lruvec, struct scan_control *sc)
++{
++	bool success;
++
++	if (!sc->may_unmap && page_mapped(page))
++		return false;
++
++	if (!(sc->may_writepage && (sc->gfp_mask & __GFP_IO)) &&
++	    (PageDirty(page) || (PageAnon(page) && !PageSwapCache(page))))
++		return false;
++
++	if (!get_page_unless_zero(page))
++		return false;
++
++	if (!TestClearPageLRU(page)) {
++		put_page(page);
++		return false;
++	}
++
++	success = lru_gen_del_page(page, lruvec, true);
++	VM_BUG_ON_PAGE(!success, page);
++
++	return true;
++}
++
++static int scan_pages(struct lruvec *lruvec, struct scan_control *sc,
++		      int type, int tier, struct list_head *list)
++{
++	int gen, zone;
++	enum vm_event_item item;
++	int sorted = 0;
++	int scanned = 0;
++	int isolated = 0;
++	int remaining = MAX_BATCH_SIZE;
++	struct lrugen *lrugen = &lruvec->evictable;
++	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
++
++	VM_BUG_ON(!list_empty(list));
++
++	if (get_nr_gens(lruvec, type) == MIN_NR_GENS)
++		return 0;
++
++	gen = lru_gen_from_seq(lrugen->min_seq[type]);
++
++	for (zone = sc->reclaim_idx; zone >= 0; zone--) {
++		LIST_HEAD(moved);
++		int skipped = 0;
++		struct list_head *head = &lrugen->lists[gen][type][zone];
++
++		while (!list_empty(head)) {
++			struct page *page = lru_to_page(head);
++			int delta = thp_nr_pages(page);
++
++			VM_BUG_ON_PAGE(PageTail(page), page);
++			VM_BUG_ON_PAGE(PageUnevictable(page), page);
++			VM_BUG_ON_PAGE(PageActive(page), page);
++			VM_BUG_ON_PAGE(page_is_file_lru(page) != type, page);
++			VM_BUG_ON_PAGE(page_zonenum(page) != zone, page);
++
++			prefetchw_prev_lru_page(page, head, flags);
++
++			scanned += delta;
++
++			if (sort_page(page, lruvec, tier))
++				sorted += delta;
++			else if (isolate_page(page, lruvec, sc)) {
++				list_add(&page->lru, list);
++				isolated += delta;
++			} else {
++				list_move(&page->lru, &moved);
++				skipped += delta;
++			}
++
++			if (!--remaining || max(isolated, skipped) >= MIN_BATCH_SIZE)
++				break;
++		}
++
++		if (skipped) {
++			list_splice(&moved, head);
++			__count_zid_vm_events(PGSCAN_SKIP, zone, skipped);
++		}
++
++		if (!remaining || isolated >= MIN_BATCH_SIZE)
++			break;
++	}
++
++	item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
++	if (!cgroup_reclaim(sc)) {
++		__count_vm_events(item, isolated);
++		__count_vm_events(PGREFILL, sorted);
++	}
++	__count_memcg_events(memcg, item, isolated);
++	__count_memcg_events(memcg, PGREFILL, sorted);
++	__count_vm_events(PGSCAN_ANON + type, isolated);
++
++	/*
++	 * We may have trouble finding eligible pages due to reclaim_idx,
++	 * may_unmap and may_writepage. Check `remaining` to make sure we won't
++	 * be stuck if we aren't making enough progress.
++	 */
++	return isolated || !remaining ? scanned : 0;
++}
++
++static int get_tier_idx(struct lruvec *lruvec, int type)
++{
++	int tier;
++	struct ctrl_pos sp, pv;
++
++	/*
++	 * Ideally we don't want to evict upper tiers that have higher refaulted
++	 * %. However, we need to leave a margin for the fluctuation in
++	 * refaulted %. So we use a larger gain factor to make sure upper tiers
++	 * are indeed more active. We choose 2 because the lowest upper tier
++	 * would have twice of refaulted % of the base tier, according to their
++	 * numbers of accesses.
++	 */
++	read_ctrl_pos(lruvec, type, 0, 1, &sp);
++	for (tier = 1; tier < MAX_NR_TIERS; tier++) {
++		read_ctrl_pos(lruvec, type, tier, 2, &pv);
++		if (!positive_ctrl_err(&sp, &pv))
++			break;
++	}
++
++	return tier - 1;
++}
++
++static int get_type_to_scan(struct lruvec *lruvec, int swappiness, int *tier_idx)
++{
++	int type, tier;
++	struct ctrl_pos sp, pv;
++	int gain[ANON_AND_FILE] = { swappiness, 200 - swappiness };
++
++	/*
++	 * Compare refaulted % between the base tiers of anon and file to
++	 * determine which type to evict. Also need to compare refaulted % of
++	 * the upper tiers of the selected type with that of the base tier of
++	 * the other type to determine which tier of the selected type to evict.
++	 */
++	read_ctrl_pos(lruvec, 0, 0, gain[0], &sp);
++	read_ctrl_pos(lruvec, 1, 0, gain[1], &pv);
++	type = positive_ctrl_err(&sp, &pv);
++
++	read_ctrl_pos(lruvec, !type, 0, gain[!type], &sp);
++	for (tier = 1; tier < MAX_NR_TIERS; tier++) {
++		read_ctrl_pos(lruvec, type, tier, gain[type], &pv);
++		if (!positive_ctrl_err(&sp, &pv))
++			break;
++	}
++
++	*tier_idx = tier - 1;
++
++	return type;
++}
++
++static int isolate_pages(struct lruvec *lruvec, struct scan_control *sc, int swappiness,
++			 int *type_scanned, struct list_head *list)
++{
++	int i;
++	int type;
++	int scanned;
++	int tier = -1;
++	DEFINE_MIN_SEQ(lruvec);
++
++	VM_BUG_ON(!seq_is_valid(lruvec));
++
++	/*
++	 * Try to select a type based on generations and swappiness, and if that
++	 * fails, fall back to get_type_to_scan(). When anon and file are both
++	 * available from the same generation, swappiness 200 is interpreted as
++	 * anon first and swappiness 1 is interpreted as file first.
++	 */
++	if (!swappiness)
++		type = 1;
++	else if (min_seq[0] < min_seq[1])
++		type = 0;
++	else if (swappiness == 1)
++		type = 1;
++	else if (swappiness == 200)
++		type = 0;
++	else
++		type = get_type_to_scan(lruvec, swappiness, &tier);
++
++	for (i = !swappiness; i < ANON_AND_FILE; i++) {
++		if (tier < 0)
++			tier = get_tier_idx(lruvec, type);
++
++		scanned = scan_pages(lruvec, sc, type, tier, list);
++		if (scanned)
++			break;
++
++		type = !type;
++		tier = -1;
++	}
++
++	*type_scanned = type;
++
++	return scanned;
++}
++
++/* Main function used by the foreground, the background and the user-triggered eviction. */
++static int evict_pages(struct lruvec *lruvec, struct scan_control *sc, int swappiness)
++{
++	int type;
++	int scanned;
++	int reclaimed;
++	LIST_HEAD(list);
++	struct page *page;
++	enum vm_event_item item;
++	struct reclaim_stat stat;
++	struct mm_walk_args *args;
++	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
++	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
++
++	spin_lock_irq(&lruvec->lru_lock);
++
++	scanned = isolate_pages(lruvec, sc, swappiness, &type, &list);
++
++	if (try_to_inc_min_seq(lruvec, swappiness))
++		scanned++;
++
++	if (get_nr_gens(lruvec, 1) == MIN_NR_GENS)
++		scanned = 0;
++
++	spin_unlock_irq(&lruvec->lru_lock);
++
++	if (list_empty(&list))
++		return scanned;
++
++	reclaimed = shrink_page_list(&list, pgdat, sc, &stat, false);
++	/*
++	 * We need to prevent rejected pages from being added back to the same
++	 * lists they were isolated from. Otherwise we may risk looping on them
++	 * forever.
++	 */
++	list_for_each_entry(page, &list, lru) {
++		if (!PageReclaim(page) || !(PageDirty(page) || PageWriteback(page)))
++			SetPageActive(page);
++
++		ClearPageReferenced(page);
++		ClearPageWorkingset(page);
++	}
++
++	spin_lock_irq(&lruvec->lru_lock);
++
++	move_pages_to_lru(lruvec, &list);
++
++	args = current->reclaim_state ? current->reclaim_state->mm_walk_args : NULL;
++	if (args && args->batch_size)
++		reset_batch_size(lruvec, args);
++
++	item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
++	if (!cgroup_reclaim(sc))
++		__count_vm_events(item, reclaimed);
++	__count_memcg_events(memcg, item, reclaimed);
++	__count_vm_events(PGSTEAL_ANON + type, reclaimed);
++
++	spin_unlock_irq(&lruvec->lru_lock);
++
++	mem_cgroup_uncharge_list(&list);
++	free_unref_page_list(&list);
++
++	sc->nr_reclaimed += reclaimed;
++
++	return scanned;
++}
++
++static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, int swappiness)
++{
++	bool low;
++	long nr_to_scan;
++	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
++	int priority = sc->priority;
++	DEFINE_MAX_SEQ(lruvec);
++	DEFINE_MIN_SEQ(lruvec);
++
++	if (mem_cgroup_below_min(memcg) ||
++	    (mem_cgroup_below_low(memcg) && !sc->memcg_low_reclaim))
++		return 0;
++
++	if (sc->nr_reclaimed >= sc->nr_to_reclaim) {
++		priority = DEF_PRIORITY;
++		sc->force_deactivate = 0;
++	}
++
++	nr_to_scan = get_nr_evictable(lruvec, sc, swappiness, max_seq, min_seq, &low);
++	if (!nr_to_scan)
++		return 0;
++
++	nr_to_scan >>= priority;
++
++	if (!mem_cgroup_online(memcg))
++		nr_to_scan++;
++
++	if (!nr_to_scan)
++		return 0;
++
++	if (current_is_kswapd()) {
++		/* leave the work to lru_gen_age_node() */
++		if (max_seq - min_seq[1] < MIN_NR_GENS)
++			return 0;
++
++		if (!low)
++			sc->force_deactivate = 0;
++
++		return nr_to_scan;
++	}
++
++	if (max_seq - min_seq[1] >= MIN_NR_GENS)
++		return nr_to_scan;
++
++	/* move onto slab and other memcgs if we haven't tried them all */
++	if (!sc->force_deactivate) {
++		sc->skipped_deactivate = 1;
++		return 0;
++	}
++
++	return try_to_inc_max_seq(lruvec, sc, swappiness, max_seq, true) ? nr_to_scan : 0;
++}
++
++static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
++{
++	struct blk_plug plug;
++	long scanned = 0;
++	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
++	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
++
++	lru_add_drain();
++
++	if (current_is_kswapd())
++		current->reclaim_state->mm_walk_args = &pgdat->mm_walk_args;
++
++	blk_start_plug(&plug);
++
++	while (true) {
++		int delta;
++		int swappiness;
++		long nr_to_scan;
++
++		if (sc->may_swap)
++			swappiness = get_swappiness(memcg);
++		else if (!cgroup_reclaim(sc) && get_swappiness(memcg))
++			swappiness = 1;
++		else
++			swappiness = 0;
++
++		nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness);
++		if (!nr_to_scan)
++			break;
++
++		delta = evict_pages(lruvec, sc, swappiness);
++		if (!delta)
++			break;
++
++		scanned += delta;
++		if (scanned >= nr_to_scan)
++			break;
++
++		cond_resched();
++	}
++
++	blk_finish_plug(&plug);
++
++	if (current_is_kswapd())
++		current->reclaim_state->mm_walk_args = NULL;
++}
++
++/******************************************************************************
+  *                          state change
+  ******************************************************************************/
+ 
+@@ -4420,6 +4961,10 @@ static void lru_gen_age_node(struct pgli
+ {
+ }
+ 
++static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
++{
++}
++
+ #endif /* CONFIG_LRU_GEN */
+ 
+ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
+@@ -4433,6 +4978,11 @@ static void shrink_lruvec(struct lruvec
+ 	struct blk_plug plug;
+ 	bool scan_adjusted;
+ 
++	if (lru_gen_enabled()) {
++		lru_gen_shrink_lruvec(lruvec, sc);
++		return;
++	}
++
+ 	get_scan_count(lruvec, sc, nr);
+ 
+ 	/* Record the original scan target for proportional adjustments later */
+@@ -4906,6 +5456,9 @@ static void snapshot_refaults(struct mem
+ 	struct lruvec *target_lruvec;
+ 	unsigned long refaults;
+ 
++	if (lru_gen_enabled())
++		return;
++
+ 	target_lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
+ 	refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_ANON);
+ 	target_lruvec->refaults[0] = refaults;
+--- a/mm/workingset.c
++++ b/mm/workingset.c
+@@ -187,7 +187,6 @@ static unsigned int bucket_order __read_
+ static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
+ 			 bool workingset)
+ {
+-	eviction >>= bucket_order;
+ 	eviction &= EVICTION_MASK;
+ 	eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
+ 	eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
+@@ -212,10 +211,117 @@ static void unpack_shadow(void *shadow,
+ 
+ 	*memcgidp = memcgid;
+ 	*pgdat = NODE_DATA(nid);
+-	*evictionp = entry << bucket_order;
++	*evictionp = entry;
+ 	*workingsetp = workingset;
+ }
+ 
++#ifdef CONFIG_LRU_GEN
++
++static int page_lru_refs(struct page *page)
++{
++	unsigned long flags = READ_ONCE(page->flags);
++
++	BUILD_BUG_ON(LRU_GEN_WIDTH + LRU_REFS_WIDTH > BITS_PER_LONG - EVICTION_SHIFT);
++
++	/* see the comment on MAX_NR_TIERS */
++	return flags & BIT(PG_workingset) ? (flags & LRU_REFS_MASK) >> LRU_REFS_PGOFF : 0;
++}
++
++/* Return a token to be stored in the shadow entry of a page being evicted. */
++static void *lru_gen_eviction(struct page *page)
++{
++	int hist, tier;
++	unsigned long token;
++	unsigned long min_seq;
++	struct lruvec *lruvec;
++	struct lrugen *lrugen;
++	int type = page_is_file_lru(page);
++	int refs = page_lru_refs(page);
++	int delta = thp_nr_pages(page);
++	bool workingset = PageWorkingset(page);
++	struct mem_cgroup *memcg = page_memcg(page);
++	struct pglist_data *pgdat = page_pgdat(page);
++
++	lruvec = mem_cgroup_lruvec(memcg, pgdat);
++	lrugen = &lruvec->evictable;
++	min_seq = READ_ONCE(lrugen->min_seq[type]);
++	token = (min_seq << LRU_REFS_WIDTH) | refs;
++
++	hist = lru_hist_from_seq(min_seq);
++	tier = lru_tier_from_refs(refs + workingset);
++	atomic_long_add(delta, &lrugen->evicted[hist][type][tier]);
++
++	return pack_shadow(mem_cgroup_id(memcg), pgdat, token, workingset);
++}
++
++/* Count a refaulted page based on the token stored in its shadow entry. */
++static void lru_gen_refault(struct page *page, void *shadow)
++{
++	int hist, tier, refs;
++	int memcg_id;
++	bool workingset;
++	unsigned long token;
++	unsigned long min_seq;
++	struct lruvec *lruvec;
++	struct lrugen *lrugen;
++	struct mem_cgroup *memcg;
++	struct pglist_data *pgdat;
++	int type = page_is_file_lru(page);
++	int delta = thp_nr_pages(page);
++
++	unpack_shadow(shadow, &memcg_id, &pgdat, &token, &workingset);
++	if (page_pgdat(page) != pgdat)
++		return;
++
++	rcu_read_lock();
++	memcg = page_memcg_rcu(page);
++	if (mem_cgroup_id(memcg) != memcg_id)
++		goto unlock;
++
++	refs = token & (BIT(LRU_REFS_WIDTH) - 1);
++	if (refs && !workingset)
++		goto unlock;
++
++	token >>= LRU_REFS_WIDTH;
++	lruvec = mem_cgroup_lruvec(memcg, pgdat);
++	lrugen = &lruvec->evictable;
++	min_seq = READ_ONCE(lrugen->min_seq[type]);
++	if (token != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)))
++		goto unlock;
++
++	hist = lru_hist_from_seq(min_seq);
++	tier = lru_tier_from_refs(refs + workingset);
++	atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]);
++	mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type, delta);
++
++	/*
++	 * Tiers don't offer any protection to pages accessed via page tables.
++	 * That's what generations do. Tiers can't fully protect pages after
++	 * their numbers of accesses has exceeded the max value. Conservatively
++	 * count these two conditions as stalls even though they might not
++	 * indicate any real memory pressure.
++	 */
++	if (task_in_nonseq_fault() || refs + workingset == BIT(LRU_REFS_WIDTH)) {
++		SetPageWorkingset(page);
++		mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta);
++	}
++unlock:
++	rcu_read_unlock();
++}
++
++#else
++
++static void *lru_gen_eviction(struct page *page)
++{
++	return NULL;
++}
++
++static void lru_gen_refault(struct page *page, void *shadow)
++{
++}
++
++#endif /* CONFIG_LRU_GEN */
++
+ /**
+  * workingset_age_nonresident - age non-resident entries as LRU ages
+  * @lruvec: the lruvec that was aged
+@@ -264,10 +370,14 @@ void *workingset_eviction(struct page *p
+ 	VM_BUG_ON_PAGE(page_count(page), page);
+ 	VM_BUG_ON_PAGE(!PageLocked(page), page);
+ 
++	if (lru_gen_enabled())
++		return lru_gen_eviction(page);
++
+ 	lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
+ 	/* XXX: target_memcg can be NULL, go through lruvec */
+ 	memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
+ 	eviction = atomic_long_read(&lruvec->nonresident_age);
++	eviction >>= bucket_order;
+ 	workingset_age_nonresident(lruvec, thp_nr_pages(page));
+ 	return pack_shadow(memcgid, pgdat, eviction, PageWorkingset(page));
+ }
+@@ -296,7 +406,13 @@ void workingset_refault(struct page *pag
+ 	bool workingset;
+ 	int memcgid;
+ 
++	if (lru_gen_enabled()) {
++		lru_gen_refault(page, shadow);
++		return;
++	}
++
+ 	unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
++	eviction <<= bucket_order;
+ 
+ 	rcu_read_lock();
+ 	/*

target/linux/generic/pending-5.15/020-07-mm-multigenerational-lru-user-interface.patch

@@ -0,0 +1,496 @@
+From 5cc7fdec54e87e32b4fb0f07d84b21769d5f8d92 Mon Sep 17 00:00:00 2001
+From: Yu Zhao <[email protected]>
+Date: Mon, 25 Jan 2021 21:38:02 -0700
+Subject: [PATCH 08/10] mm: multigenerational lru: user interface
+
+Add /sys/kernel/mm/lru_gen/enabled to enable and disable the
+multigenerational lru at runtime.
+
+Add /sys/kernel/mm/lru_gen/min_ttl_ms to protect the working set of a
+given number of milliseconds. The OOM killer is invoked if this
+working set cannot be kept in memory.
+
+Add /sys/kernel/debug/lru_gen to monitor the multigenerational lru and
+invoke the aging and the eviction. This file has the following output:
+  memcg  memcg_id  memcg_path
+    node  node_id
+      min_gen  birth_time  anon_size  file_size
+      ...
+      max_gen  birth_time  anon_size  file_size
+
+min_gen is the oldest generation number and max_gen is the youngest
+generation number. birth_time is in milliseconds. anon_size and
+file_size are in pages.
+
+This file takes the following input:
+  + memcg_id node_id max_gen [swappiness] [use_bloom_filter]
+  - memcg_id node_id min_gen [swappiness] [nr_to_reclaim]
+
+The first command line invokes the aging, which scans PTEs for
+accessed pages and then creates the next generation max_gen+1. A swap
+file and a non-zero swappiness, which overrides vm.swappiness, are
+required to scan PTEs mapping anon pages. The second command line
+invokes the eviction, which evicts generations less than or equal to
+min_gen. min_gen should be less than max_gen-1 as max_gen and
+max_gen-1 are not fully aged and therefore cannot be evicted.
+Setting nr_to_reclaim to N limits the number of pages to evict.
+Setting use_bloom_filter to 0 overrides the default behavior which
+only scans PTE tables found populated. Multiple command lines are
+supported, as is concatenation with delimiters "," and ";".
+
+Signed-off-by: Yu Zhao <[email protected]>
+Tested-by: Konstantin Kharlamov <[email protected]>
+Change-Id: I4448e60029badbe347aa3b624f429b280cc3a3d3
+---
+ include/linux/nodemask.h |   1 +
+ mm/vmscan.c              | 415 +++++++++++++++++++++++++++++++++++++++
+ 2 files changed, 416 insertions(+)
+
+--- a/include/linux/nodemask.h
++++ b/include/linux/nodemask.h
+@@ -485,6 +485,7 @@ static inline int num_node_state(enum no
+ #define first_online_node	0
+ #define first_memory_node	0
+ #define next_online_node(nid)	(MAX_NUMNODES)
++#define next_memory_node(nid)	(MAX_NUMNODES)
+ #define nr_node_ids		1U
+ #define nr_online_nodes		1U
+ 
+--- a/mm/vmscan.c
++++ b/mm/vmscan.c
+@@ -53,6 +53,8 @@
+ #include <linux/memory.h>
+ #include <linux/pagewalk.h>
+ #include <linux/shmem_fs.h>
++#include <linux/ctype.h>
++#include <linux/debugfs.h>
+ 
+ #include <asm/tlbflush.h>
+ #include <asm/div64.h>
+@@ -4882,6 +4884,413 @@ unlock:
+ }
+ 
+ /******************************************************************************
++ *                          sysfs interface
++ ******************************************************************************/
++
++static ssize_t show_min_ttl(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
++{
++	return sprintf(buf, "%u\n", jiffies_to_msecs(READ_ONCE(lru_gen_min_ttl)));
++}
++
++static ssize_t store_min_ttl(struct kobject *kobj, struct kobj_attribute *attr,
++			     const char *buf, size_t len)
++{
++	unsigned int msecs;
++
++	if (kstrtouint(buf, 10, &msecs))
++		return -EINVAL;
++
++	WRITE_ONCE(lru_gen_min_ttl, msecs_to_jiffies(msecs));
++
++	return len;
++}
++
++static struct kobj_attribute lru_gen_min_ttl_attr = __ATTR(
++	min_ttl_ms, 0644, show_min_ttl, store_min_ttl
++);
++
++static ssize_t show_enable(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
++{
++	return snprintf(buf, PAGE_SIZE, "%d\n", lru_gen_enabled());
++}
++
++static ssize_t store_enable(struct kobject *kobj, struct kobj_attribute *attr,
++			    const char *buf, size_t len)
++{
++	bool enable;
++
++	if (kstrtobool(buf, &enable))
++		return -EINVAL;
++
++	lru_gen_change_state(enable, true, false);
++
++	return len;
++}
++
++static struct kobj_attribute lru_gen_enabled_attr = __ATTR(
++	enabled, 0644, show_enable, store_enable
++);
++
++static struct attribute *lru_gen_attrs[] = {
++	&lru_gen_min_ttl_attr.attr,
++	&lru_gen_enabled_attr.attr,
++	NULL
++};
++
++static struct attribute_group lru_gen_attr_group = {
++	.name = "lru_gen",
++	.attrs = lru_gen_attrs,
++};
++
++/******************************************************************************
++ *                          debugfs interface
++ ******************************************************************************/
++
++static void *lru_gen_seq_start(struct seq_file *m, loff_t *pos)
++{
++	struct mem_cgroup *memcg;
++	loff_t nr_to_skip = *pos;
++
++	m->private = kvmalloc(PATH_MAX, GFP_KERNEL);
++	if (!m->private)
++		return ERR_PTR(-ENOMEM);
++
++	memcg = mem_cgroup_iter(NULL, NULL, NULL);
++	do {
++		int nid;
++
++		for_each_node_state(nid, N_MEMORY) {
++			if (!nr_to_skip--)
++				return get_lruvec(nid, memcg);
++		}
++	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
++
++	return NULL;
++}
++
++static void lru_gen_seq_stop(struct seq_file *m, void *v)
++{
++	if (!IS_ERR_OR_NULL(v))
++		mem_cgroup_iter_break(NULL, lruvec_memcg(v));
++
++	kvfree(m->private);
++	m->private = NULL;
++}
++
++static void *lru_gen_seq_next(struct seq_file *m, void *v, loff_t *pos)
++{
++	int nid = lruvec_pgdat(v)->node_id;
++	struct mem_cgroup *memcg = lruvec_memcg(v);
++
++	++*pos;
++
++	nid = next_memory_node(nid);
++	if (nid == MAX_NUMNODES) {
++		memcg = mem_cgroup_iter(NULL, memcg, NULL);
++		if (!memcg)
++			return NULL;
++
++		nid = first_memory_node;
++	}
++
++	return get_lruvec(nid, memcg);
++}
++
++static void lru_gen_seq_show_full(struct seq_file *m, struct lruvec *lruvec,
++				  unsigned long max_seq, unsigned long *min_seq,
++				  unsigned long seq)
++{
++	int i;
++	int type, tier;
++	int hist = lru_hist_from_seq(seq);
++	struct lrugen *lrugen = &lruvec->evictable;
++
++	for (tier = 0; tier < MAX_NR_TIERS; tier++) {
++		seq_printf(m, "            %10d", tier);
++		for (type = 0; type < ANON_AND_FILE; type++) {
++			unsigned long n[3] = {};
++
++			if (seq == max_seq) {
++				n[0] = READ_ONCE(lrugen->avg_refaulted[type][tier]);
++				n[1] = READ_ONCE(lrugen->avg_total[type][tier]);
++
++				seq_printf(m, " %10luR %10luT %10lu ", n[0], n[1], n[2]);
++			} else if (seq == min_seq[type] || NR_HIST_GENS > 1) {
++				n[0] = atomic_long_read(&lrugen->refaulted[hist][type][tier]);
++				n[1] = atomic_long_read(&lrugen->evicted[hist][type][tier]);
++				if (tier)
++					n[2] = READ_ONCE(lrugen->protected[hist][type][tier - 1]);
++
++				seq_printf(m, " %10lur %10lue %10lup", n[0], n[1], n[2]);
++			} else
++				seq_puts(m, "          0           0           0 ");
++		}
++		seq_putc(m, '\n');
++	}
++
++	seq_puts(m, "                      ");
++	for (i = 0; i < NR_MM_STATS; i++) {
++		if (seq == max_seq && NR_HIST_GENS == 1)
++			seq_printf(m, " %10lu%c", READ_ONCE(lruvec->mm_walk.stats[hist][i]),
++				   toupper(MM_STAT_CODES[i]));
++		else if (seq != max_seq && NR_HIST_GENS > 1)
++			seq_printf(m, " %10lu%c", READ_ONCE(lruvec->mm_walk.stats[hist][i]),
++				   MM_STAT_CODES[i]);
++		else
++			seq_puts(m, "          0 ");
++	}
++	seq_putc(m, '\n');
++}
++
++static int lru_gen_seq_show(struct seq_file *m, void *v)
++{
++	unsigned long seq;
++	bool full = !debugfs_real_fops(m->file)->write;
++	struct lruvec *lruvec = v;
++	struct lrugen *lrugen = &lruvec->evictable;
++	int nid = lruvec_pgdat(lruvec)->node_id;
++	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
++	DEFINE_MAX_SEQ(lruvec);
++	DEFINE_MIN_SEQ(lruvec);
++
++	if (nid == first_memory_node) {
++		const char *path = memcg ? m->private : "";
++
++#ifdef CONFIG_MEMCG
++		if (memcg)
++			cgroup_path(memcg->css.cgroup, m->private, PATH_MAX);
++#endif
++		seq_printf(m, "memcg %5hu %s\n", mem_cgroup_id(memcg), path);
++	}
++
++	seq_printf(m, " node %5d\n", nid);
++
++	if (!full)
++		seq = min_seq[0];
++	else if (max_seq >= MAX_NR_GENS)
++		seq = max_seq - MAX_NR_GENS + 1;
++	else
++		seq = 0;
++
++	for (; seq <= max_seq; seq++) {
++		int gen, type, zone;
++		unsigned int msecs;
++
++		gen = lru_gen_from_seq(seq);
++		msecs = jiffies_to_msecs(jiffies - READ_ONCE(lrugen->timestamps[gen]));
++
++		seq_printf(m, " %10lu %10u", seq, msecs);
++
++		for (type = 0; type < ANON_AND_FILE; type++) {
++			long size = 0;
++
++			if (seq < min_seq[type]) {
++				seq_puts(m, "         -0 ");
++				continue;
++			}
++
++			for (zone = 0; zone < MAX_NR_ZONES; zone++)
++				size += READ_ONCE(lrugen->sizes[gen][type][zone]);
++
++			seq_printf(m, " %10lu ", max(size, 0L));
++		}
++
++		seq_putc(m, '\n');
++
++		if (full)
++			lru_gen_seq_show_full(m, lruvec, max_seq, min_seq, seq);
++	}
++
++	return 0;
++}
++
++static const struct seq_operations lru_gen_seq_ops = {
++	.start = lru_gen_seq_start,
++	.stop = lru_gen_seq_stop,
++	.next = lru_gen_seq_next,
++	.show = lru_gen_seq_show,
++};
++
++static int run_aging(struct lruvec *lruvec, struct scan_control *sc, int swappiness,
++		     unsigned long seq, bool use_filter)
++{
++	DEFINE_MAX_SEQ(lruvec);
++
++	if (seq == max_seq)
++		try_to_inc_max_seq(lruvec, sc, swappiness, max_seq, use_filter);
++
++	return seq > max_seq ? -EINVAL : 0;
++}
++
++static int run_eviction(struct lruvec *lruvec, struct scan_control *sc, int swappiness,
++			unsigned long seq, unsigned long nr_to_reclaim)
++{
++	struct blk_plug plug;
++	int err = -EINTR;
++	DEFINE_MAX_SEQ(lruvec);
++
++	if (seq >= max_seq - 1)
++		return -EINVAL;
++
++	sc->nr_reclaimed = 0;
++
++	blk_start_plug(&plug);
++
++	while (!signal_pending(current)) {
++		DEFINE_MIN_SEQ(lruvec);
++
++		if (seq < min_seq[!swappiness] || sc->nr_reclaimed >= nr_to_reclaim ||
++		    !evict_pages(lruvec, sc, swappiness)) {
++			err = 0;
++			break;
++		}
++
++		cond_resched();
++	}
++
++	blk_finish_plug(&plug);
++
++	return err;
++}
++
++static int run_cmd(char cmd, int memcg_id, int nid, struct scan_control *sc,
++		   int swappiness, unsigned long seq, unsigned long opt)
++{
++	struct lruvec *lruvec;
++	int err = -EINVAL;
++	struct mem_cgroup *memcg = NULL;
++
++	if (!mem_cgroup_disabled()) {
++		rcu_read_lock();
++		memcg = mem_cgroup_from_id(memcg_id);
++#ifdef CONFIG_MEMCG
++		if (memcg && !css_tryget(&memcg->css))
++			memcg = NULL;
++#endif
++		rcu_read_unlock();
++
++		if (!memcg)
++			goto done;
++	}
++	if (memcg_id != mem_cgroup_id(memcg))
++		goto done;
++
++	if (nid < 0 || nid >= MAX_NUMNODES || !node_state(nid, N_MEMORY))
++		goto done;
++
++	lruvec = get_lruvec(nid, memcg);
++
++	if (swappiness < 0)
++		swappiness = get_swappiness(memcg);
++	else if (swappiness > 200)
++		goto done;
++
++	switch (cmd) {
++	case '+':
++		err = run_aging(lruvec, sc, swappiness, seq, opt);
++		break;
++	case '-':
++		err = run_eviction(lruvec, sc, swappiness, seq, opt);
++		break;
++	}
++done:
++	mem_cgroup_put(memcg);
++
++	return err;
++}
++
++static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
++				 size_t len, loff_t *pos)
++{
++	void *buf;
++	char *cur, *next;
++	unsigned int flags;
++	int err = 0;
++	struct scan_control sc = {
++		.may_writepage = 1,
++		.may_unmap = 1,
++		.may_swap = 1,
++		.reclaim_idx = MAX_NR_ZONES - 1,
++		.gfp_mask = GFP_KERNEL,
++	};
++
++	buf = kvmalloc(len + 1, GFP_KERNEL);
++	if (!buf)
++		return -ENOMEM;
++
++	if (copy_from_user(buf, src, len)) {
++		kvfree(buf);
++		return -EFAULT;
++	}
++
++	next = buf;
++	next[len] = '\0';
++
++	sc.reclaim_state.mm_walk_args = alloc_mm_walk_args();
++	if (!sc.reclaim_state.mm_walk_args) {
++		kvfree(buf);
++		return -ENOMEM;
++	}
++
++	flags = memalloc_noreclaim_save();
++	set_task_reclaim_state(current, &sc.reclaim_state);
++
++	while ((cur = strsep(&next, ",;\n"))) {
++		int n;
++		int end;
++		char cmd;
++		unsigned int memcg_id;
++		unsigned int nid;
++		unsigned long seq;
++		unsigned int swappiness = -1;
++		unsigned long opt = -1;
++
++		cur = skip_spaces(cur);
++		if (!*cur)
++			continue;
++
++		n = sscanf(cur, "%c %u %u %lu %n %u %n %lu %n", &cmd, &memcg_id, &nid,
++			   &seq, &end, &swappiness, &end, &opt, &end);
++		if (n < 4 || cur[end]) {
++			err = -EINVAL;
++			break;
++		}
++
++		err = run_cmd(cmd, memcg_id, nid, &sc, swappiness, seq, opt);
++		if (err)
++			break;
++	}
++
++	set_task_reclaim_state(current, NULL);
++	memalloc_noreclaim_restore(flags);
++
++	free_mm_walk_args(sc.reclaim_state.mm_walk_args);
++	kvfree(buf);
++
++	return err ? : len;
++}
++
++static int lru_gen_seq_open(struct inode *inode, struct file *file)
++{
++	return seq_open(file, &lru_gen_seq_ops);
++}
++
++static const struct file_operations lru_gen_rw_fops = {
++	.open = lru_gen_seq_open,
++	.read = seq_read,
++	.write = lru_gen_seq_write,
++	.llseek = seq_lseek,
++	.release = seq_release,
++};
++
++static const struct file_operations lru_gen_ro_fops = {
++	.open = lru_gen_seq_open,
++	.read = seq_read,
++	.llseek = seq_lseek,
++	.release = seq_release,
++};
++
++/******************************************************************************
+  *                          initialization
+  ******************************************************************************/
+ 
+@@ -4951,6 +5360,12 @@ static int __init init_lru_gen(void)
+ 	BUILD_BUG_ON(BIT(LRU_GEN_WIDTH) <= MAX_NR_GENS);
+ 	BUILD_BUG_ON(sizeof(MM_STAT_CODES) != NR_MM_STATS + 1);
+ 
++	if (sysfs_create_group(mm_kobj, &lru_gen_attr_group))
++		pr_err("lru_gen: failed to create sysfs group\n");
++
++	debugfs_create_file("lru_gen", 0644, NULL, NULL, &lru_gen_rw_fops);
++	debugfs_create_file("lru_gen_full", 0444, NULL, NULL, &lru_gen_ro_fops);
++
+ 	return 0;
+ };
+ late_initcall(init_lru_gen);

target/linux/generic/pending-5.15/020-08-mm-multigenerational-lru-Kconfig.patch

@@ -0,0 +1,80 @@
+From 3008095eb835d207dd7e5b60899aad17f32aa9f7 Mon Sep 17 00:00:00 2001
+From: Yu Zhao <[email protected]>
+Date: Mon, 25 Jan 2021 21:47:24 -0700
+Subject: [PATCH 09/10] mm: multigenerational lru: Kconfig
+
+Add configuration options for the multigenerational lru.
+
+Signed-off-by: Yu Zhao <[email protected]>
+Tested-by: Konstantin Kharlamov <[email protected]>
+Change-Id: Ic74ea07f8fb5f56e6904a1b80c3c286bc2911635
+---
+ mm/Kconfig | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ 1 file changed, 59 insertions(+)
+
+--- a/mm/Kconfig
++++ b/mm/Kconfig
+@@ -899,4 +899,63 @@ config SECRETMEM
+ 
+ source "mm/damon/Kconfig"
+ 
++# the multigenerational lru {
++config LRU_GEN
++	bool "Multigenerational LRU"
++	depends on MMU
++	# the following options may leave not enough spare bits in page->flags
++	depends on !MAXSMP && (64BIT || !SPARSEMEM || SPARSEMEM_VMEMMAP)
++	help
++	  A high performance LRU implementation to heavily overcommit workloads
++	  that are not IO bound. See Documentation/vm/multigen_lru.rst for
++	  details.
++
++	  Warning: do not enable this option unless you plan to use it because
++	  it introduces a small per-process and per-memcg and per-node memory
++	  overhead.
++
++config LRU_GEN_ENABLED
++	bool "Turn on by default"
++	depends on LRU_GEN
++	help
++	  The default value of /sys/kernel/mm/lru_gen/enabled is 0. This option
++	  changes it to 1.
++
++	  Warning: the default value is the fast path. See
++	  Documentation/static-keys.txt for details.
++
++config LRU_GEN_STATS
++	bool "Full stats for debugging"
++	depends on LRU_GEN
++	help
++	  This option keeps full stats for each generation, which can be read
++	  from /sys/kernel/debug/lru_gen_full.
++
++	  Warning: do not enable this option unless you plan to use it because
++	  it introduces an additional small per-process and per-memcg and
++	  per-node memory overhead.
++
++config NR_LRU_GENS
++	int "Max number of generations"
++	depends on LRU_GEN
++	range 4 31
++	default 7
++	help
++	  This will use order_base_2(N+1) spare bits from page flags.
++
++	  Warning: do not use numbers larger than necessary because each
++	  generation introduces a small per-node and per-memcg memory overhead.
++
++config TIERS_PER_GEN
++	int "Number of tiers per generation"
++	depends on LRU_GEN
++	range 2 5
++	default 4
++	help
++	  This will use N-2 spare bits from page flags.
++
++	  Larger values generally offer better protection to active pages under
++	  heavy buffered I/O workloads.
++# }
++
+ endmenu

target/linux/generic/pending-5.15/020-09-mm-multigenerational-lru-documentation.patch

@@ -0,0 +1,161 @@
+From f59c618ed70a1e48accc4cad91a200966f2569c9 Mon Sep 17 00:00:00 2001
+From: Yu Zhao <[email protected]>
+Date: Tue, 2 Feb 2021 01:27:45 -0700
+Subject: [PATCH 10/10] mm: multigenerational lru: documentation
+
+Add Documentation/vm/multigen_lru.rst.
+
+Signed-off-by: Yu Zhao <[email protected]>
+Tested-by: Konstantin Kharlamov <[email protected]>
+Change-Id: I1902178bcbb5adfa0a748c4d284a6456059bdd7e
+---
+ Documentation/vm/index.rst        |   1 +
+ Documentation/vm/multigen_lru.rst | 132 ++++++++++++++++++++++++++++++
+ 2 files changed, 133 insertions(+)
+ create mode 100644 Documentation/vm/multigen_lru.rst
+
+--- a/Documentation/vm/index.rst
++++ b/Documentation/vm/index.rst
+@@ -17,6 +17,7 @@ various features of the Linux memory man
+ 
+    swap_numa
+    zswap
++   multigen_lru
+ 
+ Kernel developers MM documentation
+ ==================================
+--- /dev/null
++++ b/Documentation/vm/multigen_lru.rst
+@@ -0,0 +1,132 @@
++.. SPDX-License-Identifier: GPL-2.0
++
++=====================
++Multigenerational LRU
++=====================
++
++Quick Start
++===========
++Build Configurations
++--------------------
++:Required: Set ``CONFIG_LRU_GEN=y``.
++
++:Optional: Set ``CONFIG_LRU_GEN_ENABLED=y`` to turn the feature on by
++ default.
++
++Runtime Configurations
++----------------------
++:Required: Write ``1`` to ``/sys/kernel/mm/lru_gen/enable`` if the
++ feature was not turned on by default.
++
++:Optional: Write ``N`` to ``/sys/kernel/mm/lru_gen/min_ttl_ms`` to
++ protect the working set of ``N`` milliseconds. The OOM killer is
++ invoked if this working set cannot be kept in memory.
++
++:Optional: Read ``/sys/kernel/debug/lru_gen`` to confirm the feature
++ is turned on. This file has the following output:
++
++::
++
++  memcg  memcg_id  memcg_path
++    node  node_id
++      min_gen  birth_time  anon_size  file_size
++      ...
++      max_gen  birth_time  anon_size  file_size
++
++``min_gen`` is the oldest generation number and ``max_gen`` is the
++youngest generation number. ``birth_time`` is in milliseconds.
++``anon_size`` and ``file_size`` are in pages.
++
++Phones/Laptops/Workstations
++---------------------------
++No additional configurations required.
++
++Servers/Data Centers
++--------------------
++:To support more generations: Change ``CONFIG_NR_LRU_GENS`` to a
++ larger number.
++
++:To support more tiers: Change ``CONFIG_TIERS_PER_GEN`` to a larger
++ number.
++
++:To support full stats: Set ``CONFIG_LRU_GEN_STATS=y``.
++
++:Working set estimation: Write ``+ memcg_id node_id max_gen
++ [swappiness] [use_bloom_filter]`` to ``/sys/kernel/debug/lru_gen`` to
++ invoke the aging, which scans PTEs for accessed pages and then
++ creates the next generation ``max_gen+1``. A swap file and a non-zero
++ ``swappiness``, which overrides ``vm.swappiness``, are required to
++ scan PTEs mapping anon pages. Set ``use_bloom_filter`` to 0 to
++ override the default behavior which only scans PTE tables found
++ populated.
++
++:Proactive reclaim: Write ``- memcg_id node_id min_gen [swappiness]
++ [nr_to_reclaim]`` to ``/sys/kernel/debug/lru_gen`` to invoke the
++ eviction, which evicts generations less than or equal to ``min_gen``.
++ ``min_gen`` should be less than ``max_gen-1`` as ``max_gen`` and
++ ``max_gen-1`` are not fully aged and therefore cannot be evicted.
++ Use ``nr_to_reclaim`` to limit the number of pages to evict. Multiple
++ command lines are supported, so does concatenation with delimiters
++ ``,`` and ``;``.
++
++Framework
++=========
++For each ``lruvec``, evictable pages are divided into multiple
++generations. The youngest generation number is stored in
++``lrugen->max_seq`` for both anon and file types as they are aged on
++an equal footing. The oldest generation numbers are stored in
++``lrugen->min_seq[]`` separately for anon and file types as clean
++file pages can be evicted regardless of swap and writeback
++constraints. These three variables are monotonically increasing.
++Generation numbers are truncated into
++``order_base_2(CONFIG_NR_LRU_GENS+1)`` bits in order to fit into
++``page->flags``. The sliding window technique is used to prevent
++truncated generation numbers from overlapping. Each truncated
++generation number is an index to an array of per-type and per-zone
++lists ``lrugen->lists``.
++
++Each generation is divided into multiple tiers. Tiers represent
++different ranges of numbers of accesses from file descriptors only.
++Pages accessed ``N`` times via file descriptors belong to tier
++``order_base_2(N)``. Each generation contains at most
++``CONFIG_TIERS_PER_GEN`` tiers, and they require additional
++``CONFIG_TIERS_PER_GEN-2`` bits in ``page->flags``. In contrast to
++moving between generations which requires list operations, moving
++between tiers only involves operations on ``page->flags`` and
++therefore has a negligible cost. A feedback loop modeled after the PID
++controller monitors refaulted % across all tiers and decides when to
++protect pages from which tiers.
++
++The framework comprises two conceptually independent components: the
++aging and the eviction, which can be invoked separately from user
++space for the purpose of working set estimation and proactive reclaim.
++
++Aging
++-----
++The aging produces young generations. Given an ``lruvec``, the aging
++traverses ``lruvec_memcg()->mm_list`` and calls ``walk_page_range()``
++to scan PTEs for accessed pages (a ``mm_struct`` list is maintained
++for each ``memcg``). Upon finding one, the aging updates its
++generation number to ``max_seq`` (modulo ``CONFIG_NR_LRU_GENS``).
++After each round of traversal, the aging increments ``max_seq``. The
++aging is due when ``min_seq[]`` reaches ``max_seq-1``.
++
++Eviction
++--------
++The eviction consumes old generations. Given an ``lruvec``, the
++eviction scans pages on the per-zone lists indexed by anon and file
++``min_seq[]`` (modulo ``CONFIG_NR_LRU_GENS``). It first tries to
++select a type based on the values of ``min_seq[]``. If they are
++equal, it selects the type that has a lower refaulted %. The eviction
++sorts a page according to its updated generation number if the aging
++has found this page accessed. It also moves a page to the next
++generation if this page is from an upper tier that has a higher
++refaulted % than the base tier. The eviction increments ``min_seq[]``
++of a selected type when it finds all the per-zone lists indexed by
++``min_seq[]`` of this selected type are empty.
++
++To-do List
++==========
++KVM Optimization
++----------------
++Support shadow page table walk.