lib/config, lib/model: Limit concurrent pulls (fixes #5914) (#6290)

Adds a new folder state "Waiting to Sync" in the same vein as the
existing "Waiting to Scan". This vastly improves performances in the
rare cases when there are lots and lots of folders operating.

gui/default/index.html

@@ -313,7 +313,7 @@
                   <span ng-switch-when="paused"><span class="hidden-xs" translate>Paused</span><span class="visible-xs" aria-label="{{'Paused' | translate}}"><i class="fas fa-fw fa-pause"></i></span></span>
                   <span ng-switch-when="unknown"><span class="hidden-xs" translate>Unknown</span><span class="visible-xs" aria-label="{{'Unknown' | translate}}"><i class="fas fa-fw fa-question-circle"></i></span></span>
                   <span ng-switch-when="unshared"><span class="hidden-xs" translate>Unshared</span><span class="visible-xs" aria-label="{{'Unshared' | translate}}"><i class="fas fa-fw fa-unlink"></i></span></span>
-                  <span ng-switch-when="scan-waiting"><span class="hidden-xs" translate>Waiting to scan</span><span class="visible-xs" aria-label="{{'Waiting to scan' | translate}}"><i class="fas fa-fw fa-hourglass-half"></i></span></span>
+                  <span ng-switch-when="scan-waiting"><span class="hidden-xs" translate>Waiting to Scan</span><span class="visible-xs" aria-label="{{'Waiting to Scan' | translate}}"><i class="fas fa-fw fa-hourglass-half"></i></span></span>
                   <span ng-switch-when="stopped"><span class="hidden-xs" translate>Stopped</span><span class="visible-xs" aria-label="{{'Stopped' | translate}}"><i class="fas fa-fw fa-stop"></i></span></span>
                   <span ng-switch-when="scanning">
                     <span class="hidden-xs" translate>Scanning</span>
@@ -324,6 +324,10 @@
                   </span>
                   <span ng-switch-when="idle"><span class="hidden-xs" translate>Up to Date</span><span class="visible-xs" aria-label="{{'Up to Date' | translate}}"><i class="fas fa-fw fa-check"></i></span></span>
                   <span ng-switch-when="localadditions"><span class="hidden-xs" translate>Local Additions</span><span class="visible-xs" aria-label="{{'Local Additions' | translate}}"><i class="fas fa-fw fa-check"></i></span></span>
+                  <span ng-switch-when="sync-waiting">
+                    <span class="hidden-xs" translate>Waiting to Sync</span>
+                    <span class="visible-xs" aria-label="{{'Waiting to Sync' | translate}}"><i class="fas fa-fw fa-hourglass-half"></i></span>
+                  </span>
                   <span ng-switch-when="sync-preparing">
                     <span class="hidden-xs" translate>Preparing to Sync</span>
                     <span class="visible-xs" aria-label="{{'Preparing to Sync' | translate}}"><i class="fas fa-fw fa-hourglass-half"></i></span>

gui/default/syncthing/core/syncthingController.js

@@ -837,7 +837,7 @@ angular.module('syncthing.core')
             if (status === 'stopped' || status === 'outofsync' || status === 'error' || status === 'faileditems') {
                 return 'danger';
             }
-            if (status === 'unshared' || status === 'scan-waiting') {
+            if (status === 'unshared' || status === 'scan-waiting' || status === 'sync-waiting') {
                 return 'warning';
             }
 

lib/config/config.go

@@ -31,7 +31,7 @@ import (
 
 const (
 	OldestHandledVersion = 10
-	CurrentVersion       = 29
+	CurrentVersion       = 30
 	MaxRescanIntervalS   = 365 * 24 * 60 * 60
 )
 

lib/config/config_test.go

@@ -86,8 +86,13 @@ func TestDefaultValues(t *testing.T) {
 
 func TestDeviceConfig(t *testing.T) {
 	for i := OldestHandledVersion; i <= CurrentVersion; i++ {
+		cfgFile := fmt.Sprintf("testdata/v%d.xml", i)
+		if _, err := os.Stat(cfgFile); os.IsNotExist(err) {
+			continue
+		}
+
 		os.RemoveAll(filepath.Join("testdata", DefaultMarkerName))
-		wr, err := load(fmt.Sprintf("testdata/v%d.xml", i), device1)
+		wr, err := load(cfgFile, device1)
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -1127,6 +1132,27 @@ func TestRemoveDeviceWithEmptyID(t *testing.T) {
 	}
 }
 
+func TestMaxConcurrentFolders(t *testing.T) {
+	cases := []struct {
+		input  int
+		output int
+	}{
+		{input: -42, output: 0},
+		{input: -1, output: 0},
+		{input: 0, output: runtime.GOMAXPROCS(-1)},
+		{input: 1, output: 1},
+		{input: 42, output: 42},
+	}
+
+	for _, tc := range cases {
+		opts := OptionsConfiguration{RawMaxFolderConcurrency: tc.input}
+		res := opts.MaxFolderConcurrency()
+		if res != tc.output {
+			t.Errorf("Wrong MaxFolderConcurrency, %d => %d, expected %d", tc.input, res, tc.output)
+		}
+	}
+}
+
 // defaultConfigAsMap returns a valid default config as a JSON-decoded
 // map[string]interface{}. This is useful to override random elements and
 // re-encode into JSON.

lib/config/migrations.go

@@ -25,6 +25,7 @@ import (
 // update the config version. The order of migrations doesn't matter here,
 // put the newest on top for readability.
 var migrations = migrationSet{
+	{30, migrateToConfigV30},
 	{29, migrateToConfigV29},
 	{28, migrateToConfigV28},
 	{27, migrateToConfigV27},
@@ -84,6 +85,13 @@ func (m migration) apply(cfg *Configuration) {
 	cfg.Version = m.targetVersion
 }
 
+func migrateToConfigV30(cfg *Configuration) {
+	// The "max concurrent scans" option is now spelled "max folder concurrency"
+	// to be more general.
+	cfg.Options.RawMaxFolderConcurrency = cfg.Options.DeprecatedMaxConcurrentScans
+	cfg.Options.DeprecatedMaxConcurrentScans = 0
+}
+
 func migrateToConfigV29(cfg *Configuration) {
 	// The new crash reporting option should follow the state of global
 	// discovery / usage reporting, and we should display an appropriate

lib/config/optionsconfiguration.go

@@ -8,6 +8,7 @@ package config
 
 import (
 	"fmt"
+	"runtime"
 
 	"github.com/syncthing/syncthing/lib/rand"
 	"github.com/syncthing/syncthing/lib/util"
@@ -52,7 +53,7 @@ type OptionsConfiguration struct {
 	TrafficClass            int      `xml:"trafficClass" json:"trafficClass"`
 	DefaultFolderPath       string   `xml:"defaultFolderPath" json:"defaultFolderPath" default:"~"`
 	SetLowPriority          bool     `xml:"setLowPriority" json:"setLowPriority" default:"true"`
-	MaxConcurrentScans      int      `xml:"maxConcurrentScans" json:"maxConcurrentScans"`
+	RawMaxFolderConcurrency int      `xml:"maxFolderConcurrency" json:"maxFolderConcurrency"`
 	CRURL                   string   `xml:"crashReportingURL" json:"crURL" default:"https://crash.syncthing.net/newcrash"` // crash reporting URL
 	CREnabled               bool     `xml:"crashReportingEnabled" json:"crashReportingEnabled" default:"true" restart:"true"`
 	StunKeepaliveStartS     int      `xml:"stunKeepaliveStartS" json:"stunKeepaliveStartS" default:"180"` // 0 for off
@@ -66,6 +67,7 @@ type OptionsConfiguration struct {
 	DeprecatedUPnPTimeoutS       int      `xml:"upnpTimeoutSeconds,omitempty" json:"-"`
 	DeprecatedRelayServers       []string `xml:"relayServer,omitempty" json:"-"`
 	DeprecatedMinHomeDiskFreePct float64  `xml:"minHomeDiskFreePct,omitempty" json:"-"`
+	DeprecatedMaxConcurrentScans int      `xml:"maxConcurrentScans,omitempty" json:"-"`
 }
 
 func (opts OptionsConfiguration) Copy() OptionsConfiguration {
@@ -152,3 +154,24 @@ func (opts OptionsConfiguration) GlobalDiscoveryServers() []string {
 	}
 	return util.UniqueTrimmedStrings(servers)
 }
+
+func (opts OptionsConfiguration) MaxFolderConcurrency() int {
+	// If a value is set, trust that.
+	if opts.RawMaxFolderConcurrency > 0 {
+		return opts.RawMaxFolderConcurrency
+	}
+	if opts.RawMaxFolderConcurrency < 0 {
+		// -1 etc means unlimited, which in the implementation means zero
+		return 0
+	}
+	// Otherwise default to the number of CPU cores in the system as a rough
+	// approximation of system powerfullness.
+	if n := runtime.GOMAXPROCS(-1); n > 0 {
+		return n
+	}
+	// We should never get here to begin with, but since we're here let's
+	// use some sort of reasonable compromise between the old "no limit" and
+	// getting nothing done... (Median number of folders out there at time
+	// of writing is two, 95-percentile at 12 folders.)
+	return 4 // https://xkcd.com/221/
+}

lib/config/testdata/v10.xml

@@ -1,12 +0,0 @@
-<configuration version="10">
-    <folder id="test" path="testdata" ro="true" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>b</address>
-    </device>
-</configuration>

lib/config/testdata/v11.xml

@@ -1,13 +0,0 @@
-<configuration version="11">
-    <folder id="test" path="testdata" ro="true" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFreePct>1</minDiskFreePct>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>b</address>
-    </device>
-</configuration>

lib/config/testdata/v12.xml

@@ -1,14 +0,0 @@
-<configuration version="12">
-    <folder id="test" path="testdata" ro="true" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFreePct>1</minDiskFreePct>
-        <maxConflicts>-1</maxConflicts>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v13.xml

@@ -1,14 +0,0 @@
-<configuration version="13">
-    <folder id="test" path="testdata" ro="true" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFreePct>1</minDiskFreePct>
-        <maxConflicts>-1</maxConflicts>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v14.xml

@@ -1,14 +0,0 @@
-<configuration version="14">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFreePct>1</minDiskFreePct>
-        <maxConflicts>-1</maxConflicts>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v15.xml

@@ -1,14 +0,0 @@
-<configuration version="15">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFreePct>1</minDiskFreePct>
-        <maxConflicts>-1</maxConflicts>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v16.xml

@@ -1,14 +0,0 @@
-<configuration version="16">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFreePct>1</minDiskFreePct>
-        <maxConflicts>-1</maxConflicts>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v17.xml

@@ -1,15 +0,0 @@
-<configuration version="17">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFreePct>1</minDiskFreePct>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v18.xml

@@ -1,15 +0,0 @@
-<configuration version="18">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFreePct>1</minDiskFreePct>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v19.xml

@@ -1,15 +0,0 @@
-<configuration version="19">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFreePct>1</minDiskFreePct>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v20.xml

@@ -1,15 +0,0 @@
-<configuration version="20">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFree unit="%">1</minDiskFree>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v21.xml

@@ -1,15 +0,0 @@
-<configuration version="21">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFree unit="%">1</minDiskFree>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v23.xml

@@ -1,16 +0,0 @@
-<configuration version="22">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <filesystemType>basic</filesystemType>
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFree unit="%">1</minDiskFree>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v24.xml

@@ -1,16 +0,0 @@
-<configuration version="22">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" autoNormalize="true">
-        <filesystemType>basic</filesystemType>
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFree unit="%">1</minDiskFree>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v25.xml

@@ -1,16 +0,0 @@
-<configuration version="25">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" fsWatcherEnabled="false" fsWatcherDelayS="10" autoNormalize="true">
-        <filesystemType>basic</filesystemType>
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFree unit="%">1</minDiskFree>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v26.xml

@@ -1,16 +0,0 @@
-<configuration version="26">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" fsWatcherEnabled="false" fsWatcherDelayS="10" autoNormalize="true">
-        <filesystemType>basic</filesystemType>
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFree unit="%">1</minDiskFree>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v27.xml

@@ -1,16 +0,0 @@
-<configuration version="27">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" fsWatcherEnabled="false" fsWatcherDelayS="10" autoNormalize="true">
-        <filesystemType>basic</filesystemType>
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFree unit="%">1</minDiskFree>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v28.xml

@@ -1,16 +0,0 @@
-<configuration version="28">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" fsWatcherEnabled="false" fsWatcherDelayS="10" autoNormalize="true">
-        <filesystemType>basic</filesystemType>
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFree unit="%">1</minDiskFree>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v29.xml

@@ -1,16 +0,0 @@
-<configuration version="28">
-    <folder id="test" path="testdata" type="readonly" ignorePerms="false" rescanIntervalS="600" fsWatcherEnabled="false" fsWatcherDelayS="10" autoNormalize="true">
-        <filesystemType>basic</filesystemType>
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-        <minDiskFree unit="%">1</minDiskFree>
-        <maxConflicts>-1</maxConflicts>
-        <fsync>true</fsync>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>tcp://a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>tcp://b</address>
-    </device>
-</configuration>

lib/config/testdata/v6.xml

@@ -1,12 +0,0 @@
-<configuration version="6">
-    <folder id="test" path="testdata" ro="true" ignorePerms="false" rescanIntervalS="600">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="true">
-        <address>a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="true">
-        <address>b</address>
-    </device>
-</configuration>

lib/config/testdata/v7.xml

@@ -1,12 +0,0 @@
-<configuration version="7">
-    <folder id="test" path="testdata" ro="true" ignorePerms="false" rescanIntervalS="600">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="true">
-        <address>a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="true">
-        <address>b</address>
-    </device>
-</configuration>

lib/config/testdata/v8.xml

@@ -1,12 +0,0 @@
-<configuration version="8">
-    <folder id="test" path="testdata" ro="true" ignorePerms="false" rescanIntervalS="600">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="true">
-        <address>a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="true">
-        <address>b</address>
-    </device>
-</configuration>

lib/config/testdata/v9.xml

@@ -1,12 +0,0 @@
-<configuration version="9">
-    <folder id="test" path="testdata" ro="true" ignorePerms="false" rescanIntervalS="600">
-        <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR"></device>
-        <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2"></device>
-    </folder>
-    <device id="AIR6LPZ-7K4PTTV-UXQSMUU-CPQ5YWH-OEDFIIQ-JUG777G-2YQXXR5-YD6AWQR" name="node one" compression="metadata">
-        <address>a</address>
-    </device>
-    <device id="P56IOI7-MZJNU2Y-IQGDREY-DM2MGTI-MGL3BXN-PQ6W5BM-TBBZ4TJ-XZWICQ2" name="node two" compression="metadata">
-        <address>b</address>
-    </device>
-</configuration>

lib/model/folder.go

@@ -33,8 +33,9 @@ import (
 	"github.com/thejerf/suture"
 )
 
-// scanLimiter limits the number of concurrent scans. A limit of zero means no limit.
-var scanLimiter = newByteSemaphore(0)
+// folderIOLimiter limits the number of concurrent I/O heavy operations,
+// such as scans and pulls. A limit of zero means no limit.
+var folderIOLimiter = newByteSemaphore(0)
 
 type folder struct {
 	suture.Service
@@ -130,7 +131,7 @@ func (f *folder) serve(ctx context.Context) {
 
 	pull := func() {
 		startTime := time.Now()
-		if f.puller.pull() {
+		if f.pull() {
 			// We're good. Don't schedule another pull and reset
 			// the pause interval.
 			pause = f.basePause()
@@ -164,7 +165,7 @@ func (f *folder) serve(ctx context.Context) {
 		case <-initialCompleted:
 			// Initial scan has completed, we should do a pull
 			initialCompleted = nil // never hit this case again
-			if !f.puller.pull() {
+			if !f.pull() {
 				// Pulling failed, try again later.
 				pullFailTimer.Reset(pause)
 			}
@@ -279,6 +280,35 @@ func (f *folder) getHealthError() error {
 	return nil
 }
 
+func (f *folder) pull() bool {
+	select {
+	case <-f.initialScanFinished:
+	default:
+		// Once the initial scan finished, a pull will be scheduled
+		return true
+	}
+
+	// If there is nothing to do, don't even enter sync-waiting state.
+	abort := true
+	snap := f.fset.Snapshot()
+	snap.WithNeed(protocol.LocalDeviceID, func(intf db.FileIntf) bool {
+		abort = false
+		return false
+	})
+	snap.Release()
+	if abort {
+		return true
+	}
+
+	f.setState(FolderSyncWaiting)
+	defer f.setState(FolderIdle)
+
+	folderIOLimiter.take(1)
+	defer folderIOLimiter.give(1)
+
+	return f.puller.pull()
+}
+
 func (f *folder) scanSubdirs(subDirs []string) error {
 	if err := f.getHealthError(); err != nil {
 		// If there is a health error we set it as the folder error. We do not
@@ -312,8 +342,8 @@ func (f *folder) scanSubdirs(subDirs []string) error {
 	f.setError(nil)
 	f.setState(FolderScanWaiting)
 
-	scanLimiter.take(1)
-	defer scanLimiter.give(1)
+	folderIOLimiter.take(1)
+	defer folderIOLimiter.give(1)
 
 	for i := range subDirs {
 		sub := osutil.NativeFilename(subDirs[i])

lib/model/folder_sendrecv.go

@@ -140,25 +140,6 @@ func newSendReceiveFolder(model *model, fset *db.FileSet, ignores *ignore.Matche
 // pull returns true if it manages to get all needed items from peers, i.e. get
 // the device in sync with the global state.
 func (f *sendReceiveFolder) pull() bool {
-	select {
-	case <-f.initialScanFinished:
-	default:
-		// Once the initial scan finished, a pull will be scheduled
-		return true
-	}
-
-	// If there is nothing to do, don't even enter pulling state.
-	abort := true
-	snap := f.fset.Snapshot()
-	snap.WithNeed(protocol.LocalDeviceID, func(intf db.FileIntf) bool {
-		abort = false
-		return false
-	})
-	snap.Release()
-	if abort {
-		return true
-	}
-
 	if err := f.CheckHealth(); err != nil {
 		l.Debugln("Skipping pull of", f.Description(), "due to folder error:", err)
 		return false

lib/model/folderstate.go

@@ -19,6 +19,7 @@ const (
 	FolderIdle folderState = iota
 	FolderScanning
 	FolderScanWaiting
+	FolderSyncWaiting
 	FolderSyncPreparing
 	FolderSyncing
 	FolderError
@@ -32,6 +33,8 @@ func (s folderState) String() string {
 		return "scanning"
 	case FolderScanWaiting:
 		return "scan-waiting"
+	case FolderSyncWaiting:
+		return "sync-waiting"
 	case FolderSyncPreparing:
 		return "sync-preparing"
 	case FolderSyncing:

lib/model/model.go

@@ -208,7 +208,7 @@ func NewModel(cfg config.Wrapper, id protocol.DeviceID, clientName, clientVersio
 		m.deviceStatRefs[devID] = stats.NewDeviceStatisticsReference(m.db, devID.String())
 	}
 	m.Add(m.progressEmitter)
-	scanLimiter.setCapacity(cfg.Options().MaxConcurrentScans)
+	folderIOLimiter.setCapacity(cfg.Options().MaxFolderConcurrency())
 
 	return m
 }
@@ -2483,7 +2483,7 @@ func (m *model) CommitConfiguration(from, to config.Configuration) bool {
 	}
 	m.fmut.Unlock()
 
-	scanLimiter.setCapacity(to.Options.MaxConcurrentScans)
+	folderIOLimiter.setCapacity(to.Options.MaxFolderConcurrency())
 
 	// Some options don't require restart as those components handle it fine
 	// by themselves. Compare the options structs containing only the

test/folders.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+
+for ((id=0;id<200;id++)); do
+cat <<EOT
+    <folder id="$id" label="" path="$id?maxsize=1000&amp;seed=$id" type="sendreceive" rescanIntervalS="3600" fsWatcherEnabled="false" fsWatcherDelayS="10" ignorePerms="false" autoNormalize="true">
+        <filesystemType>fake</filesystemType>
+        <device id="I6KAH76-66SLLLB-5PFXSOA-UFJCDZC-YAOMLEK-CP2GB32-BV5RQST-3PSROAU" introducedBy=""></device>
+        <device id="MRIW7OK-NETT3M4-N6SBWME-N25O76W-YJKVXPH-FUMQJ3S-P57B74J-GBITBAC" introducedBy=""></device>
+    </folder>
+EOT
+done