openwrt/target/linux/generic/backport-6.6/300-v6.7-arm64-swiotlb-Reduce-the-default-size-if-no-ZONE_DMA.patch

From 65033574ade97afccba074d837fd269903a83a9a Mon Sep 17 00:00:00 2001
From: Catalin Marinas <[email protected]>
Date: Thu, 5 Oct 2023 16:40:30 +0100
Subject: [PATCH] arm64: swiotlb: Reduce the default size if no ZONE_DMA
 bouncing needed

With CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC enabled, the arm64 kernel still
allocates the default SWIOTLB buffer (64MB) even if ZONE_DMA is disabled
or all the RAM fits into this zone. However, this potentially wastes a
non-negligible amount of memory on platforms with little RAM.

Reduce the SWIOTLB size to 1MB per 1GB of RAM if only needed for
kmalloc() buffer bouncing.

Signed-off-by: Catalin Marinas <[email protected]>
Suggested-by: Ross Burton <[email protected]>
Cc: Ross Burton <[email protected]>
Cc: Will Deacon <[email protected]>
Reviewed-by: Robin Murphy <[email protected]>
---
 arch/arm64/mm/init.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -16,6 +16,7 @@
 #include <linux/nodemask.h>
 #include <linux/initrd.h>
 #include <linux/gfp.h>
+#include <linux/math.h>
 #include <linux/memblock.h>
 #include <linux/sort.h>
 #include <linux/of.h>
@@ -493,8 +494,16 @@ void __init mem_init(void)
 {
 	bool swiotlb = max_pfn > PFN_DOWN(arm64_dma_phys_limit);
 
-	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC))
+	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb) {
+		/*
+		 * If no bouncing needed for ZONE_DMA, reduce the swiotlb
+		 * buffer for kmalloc() bouncing to 1MB per 1GB of RAM.
+		 */
+		unsigned long size =
+			DIV_ROUND_UP(memblock_phys_mem_size(), 1024);
+		swiotlb_adjust_size(min(swiotlb_size_or_default(), size));
 		swiotlb = true;
+	}
 
 	swiotlb_init(swiotlb, SWIOTLB_VERBOSE);