From: Michael Anthony Knyszek <mknyszek@google.com>
Date: Mon, 4 Oct 2021 19:52:48 +0000 (+0000)
Subject: runtime: update and access scavengeGoal atomically
X-Git-Tag: go1.18beta1~538
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=fc5e8cd6c9de00f8d7da645343934c548e62223e;p=gostls13.git

runtime: update and access scavengeGoal atomically

The first step toward acquiring the heap lock less frequently in the
scavenger.

Change-Id: Idc69fd8602be2c83268c155951230d60e20b42fe
Reviewed-on: https://go-review.googlesource.com/c/go/+/353973
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
---

diff --git a/src/runtime/mgcscavenge.go b/src/runtime/mgcscavenge.go
index fb9b5c8694..4edeb8739e 100644
--- a/src/runtime/mgcscavenge.go
+++ b/src/runtime/mgcscavenge.go
@@ -125,7 +125,7 @@ func gcPaceScavenger(heapGoal, lastHeapGoal uint64) {
 	// information about the heap yet) so this is fine, and avoids a fault
 	// or garbage data later.
 	if lastHeapGoal == 0 {
-		mheap_.scavengeGoal = ^uint64(0)
+		atomic.Store64(&mheap_.scavengeGoal, ^uint64(0))
 		return
 	}
 	// Compute our scavenging goal.
@@ -157,10 +157,10 @@ func gcPaceScavenger(heapGoal, lastHeapGoal uint64) {
 	// the background scavenger. We disable the background scavenger if there's
 	// less than one physical page of work to do because it's not worth it.
 	if retainedNow <= retainedGoal || retainedNow-retainedGoal < uint64(physPageSize) {
-		mheap_.scavengeGoal = ^uint64(0)
+		atomic.Store64(&mheap_.scavengeGoal, ^uint64(0))
 		return
 	}
-	mheap_.scavengeGoal = retainedGoal
+	atomic.Store64(&mheap_.scavengeGoal, retainedGoal)
 }
 
 // Sleep/wait state of the background scavenger.
@@ -299,7 +299,7 @@ func bgscavenge(c chan int) {
 			lock(&mheap_.lock)
 
 			// If background scavenging is disabled or if there's no work to do just park.
-			retained, goal := heapRetained(), mheap_.scavengeGoal
+			retained, goal := heapRetained(), atomic.Load64(&mheap_.scavengeGoal)
 			if retained <= goal {
 				unlock(&mheap_.lock)
 				return
diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go
index 057ab06b1d..f2f6e7f4cf 100644
--- a/src/runtime/mheap.go
+++ b/src/runtime/mheap.go
@@ -111,6 +111,8 @@ type mheap struct {
 	// scavengeGoal is the amount of total retained heap memory (measured by
 	// heapRetained) that the runtime will try to maintain by returning memory
 	// to the OS.
+	//
+	// Accessed atomically.
 	scavengeGoal uint64
 
 	// Page reclaimer state
@@ -1399,9 +1401,10 @@ func (h *mheap) grow(npage uintptr) bool {
 	// By scavenging inline we deal with the failure to allocate out of
 	// memory fragments by scavenging the memory fragments that are least
 	// likely to be re-used.
-	if retained := heapRetained(); retained+uint64(totalGrowth) > h.scavengeGoal {
+	scavengeGoal := atomic.Load64(&h.scavengeGoal)
+	if retained := heapRetained(); retained+uint64(totalGrowth) > scavengeGoal {
 		todo := totalGrowth
-		if overage := uintptr(retained + uint64(totalGrowth) - h.scavengeGoal); todo > overage {
+		if overage := uintptr(retained + uint64(totalGrowth) - scavengeGoal); todo > overage {
 			todo = overage
 		}
 		h.pages.scavenge(todo, false)