From: Michael Anthony Knyszek <mknyszek@google.com>
Date: Sat, 13 Aug 2022 16:37:09 +0000 (+0000)
Subject: runtime: factor out GC assist credit accounting
X-Git-Tag: go1.20rc1~664
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=987f94fa038d4a66fa174ddc4267d8718a029581;p=gostls13.git

runtime: factor out GC assist credit accounting

No-op change in preparation for arenas.

For #51317.

Change-Id: I0777f21763fcd34957b7e709580cf2b7a962ba67
Reviewed-on: https://go-review.googlesource.com/c/go/+/423365
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
---

diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index f2b93c04f4..c18ed07d49 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -895,24 +895,7 @@ func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer {
 
 	// assistG is the G to charge for this allocation, or nil if
 	// GC is not currently active.
-	var assistG *g
-	if gcBlackenEnabled != 0 {
-		// Charge the current user G for this allocation.
-		assistG = getg()
-		if assistG.m.curg != nil {
-			assistG = assistG.m.curg
-		}
-		// Charge the allocation against the G. We'll account
-		// for internal fragmentation at the end of mallocgc.
-		assistG.gcAssistBytes -= int64(size)
-
-		if assistG.gcAssistBytes < 0 {
-			// This G is in debt. Assist the GC to correct
-			// this before allocating. This must happen
-			// before disabling preemption.
-			gcAssistAlloc(assistG)
-		}
-	}
+	assistG := deductAssistCredit(size)
 
 	// Set mp.mallocing to keep from being preempted by GC.
 	mp := acquirem()
@@ -1165,6 +1148,34 @@ func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer {
 	return x
 }
 
+// deductAssistCredit reduces the current G's assist credit
+// by size bytes, and assists the GC if necessary.
+//
+// Caller must be preemptible.
+//
+// Returns the G for which the assist credit was accounted.
+func deductAssistCredit(size uintptr) *g {
+	var assistG *g
+	if gcBlackenEnabled != 0 {
+		// Charge the current user G for this allocation.
+		assistG = getg()
+		if assistG.m.curg != nil {
+			assistG = assistG.m.curg
+		}
+		// Charge the allocation against the G. We'll account
+		// for internal fragmentation at the end of mallocgc.
+		assistG.gcAssistBytes -= int64(size)
+
+		if assistG.gcAssistBytes < 0 {
+			// This G is in debt. Assist the GC to correct
+			// this before allocating. This must happen
+			// before disabling preemption.
+			gcAssistAlloc(assistG)
+		}
+	}
+	return assistG
+}
+
 // memclrNoHeapPointersChunked repeatedly calls memclrNoHeapPointers
 // on chunks of the buffer to be zeroed, with opportunities for preemption
 // along the way.  memclrNoHeapPointers contains no safepoints and also