From: Michael Pratt <mpratt@google.com>
Date: Wed, 22 Oct 2025 18:44:30 +0000 (-0400)
Subject: runtime: use new list type for spanSPMCs
X-Git-Tag: go1.26rc1~326
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=046dce0e54;p=gostls13.git

runtime: use new list type for spanSPMCs

Now that we have a reusable list type, use it to replace the custom
linked list code for spanSPMCs.

Change-Id: I6a6a636ca54f2ba4b5c7dddba607c94ebf3c3ac8
Reviewed-on: https://go-review.googlesource.com/c/go/+/714021
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
---

diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index bf9d9fd888..22150dfd17 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -195,6 +195,7 @@ func gcinit() {
 
 	work.startSema = 1
 	work.markDoneSema = 1
+	work.spanSPMCs.list.init(unsafe.Offsetof(spanSPMC{}.allnode))
 	lockInit(&work.sweepWaiters.lock, lockRankSweepWaiters)
 	lockInit(&work.assistQueue.lock, lockRankAssistQueue)
 	lockInit(&work.strongFromWeak.lock, lockRankStrongFromWeakQueue)
@@ -354,7 +355,7 @@ type workType struct {
 	// Only used if goexperiment.GreenTeaGC.
 	spanSPMCs struct {
 		lock mutex
-		all  *spanSPMC
+		list listHeadManual // *spanSPMC
 	}
 
 	// Restore 64-bit alignment on 32-bit.
diff --git a/src/runtime/mgcmark_greenteagc.go b/src/runtime/mgcmark_greenteagc.go
index 7b78611cf7..3594b33cfd 100644
--- a/src/runtime/mgcmark_greenteagc.go
+++ b/src/runtime/mgcmark_greenteagc.go
@@ -635,20 +635,9 @@ func (q *spanQueue) destroy() {
 
 	lock(&work.spanSPMCs.lock)
 
-	// Remove and free each ring.
+	// Remove, deinitialize, and free each ring.
 	for r := (*spanSPMC)(q.chain.tail.Load()); r != nil; r = (*spanSPMC)(r.prev.Load()) {
-		prev := r.allprev
-		next := r.allnext
-		if prev != nil {
-			prev.allnext = next
-		}
-		if next != nil {
-			next.allprev = prev
-		}
-		if work.spanSPMCs.all == r {
-			work.spanSPMCs.all = next
-		}
-
+		work.spanSPMCs.list.remove(unsafe.Pointer(r))
 		r.deinit()
 		mheap_.spanSPMCAlloc.free(unsafe.Pointer(r))
 	}
@@ -688,15 +677,10 @@ func (q *spanQueue) destroy() {
 type spanSPMC struct {
 	_ sys.NotInHeap
 
-	// allnext is the link to the next spanSPMC on the work.spanSPMCs list.
-	// This is used to find and free dead spanSPMCs. Protected by
-	// work.spanSPMCs.lock.
-	allnext *spanSPMC
-
-	// allprev is the link to the previous spanSPMC on the work.spanSPMCs
-	// list. This is used to find and free dead spanSPMCs. Protected by
+	// allnode is the linked list node for work.spanSPMCs list. This is
+	// used to find and free dead spanSPMCs. Protected by
 	// work.spanSPMCs.lock.
-	allprev *spanSPMC
+	allnode listNodeManual
 
 	// dead indicates whether the spanSPMC is no longer in use.
 	// Protected by the CAS to the prev field of the spanSPMC pointing
@@ -724,12 +708,7 @@ type spanSPMC struct {
 func newSpanSPMC(cap uint32) *spanSPMC {
 	lock(&work.spanSPMCs.lock)
 	r := (*spanSPMC)(mheap_.spanSPMCAlloc.alloc())
-	next := work.spanSPMCs.all
-	r.allnext = next
-	if next != nil {
-		next.allprev = r
-	}
-	work.spanSPMCs.all = r
+	work.spanSPMCs.list.push(unsafe.Pointer(r))
 	unlock(&work.spanSPMCs.lock)
 
 	// If cap < the capacity of a single physical page, round up.
@@ -765,8 +744,7 @@ func (r *spanSPMC) deinit() {
 	r.head.Store(0)
 	r.tail.Store(0)
 	r.cap = 0
-	r.allnext = nil
-	r.allprev = nil
+	r.allnode = listNodeManual{}
 }
 
 // slot returns a pointer to slot i%r.cap.
@@ -795,26 +773,16 @@ func freeDeadSpanSPMCs() {
 	// GOMAXPROCS, or if this list otherwise gets long, it would be nice to
 	// have a way to batch work that allows preemption during processing.
 	lock(&work.spanSPMCs.lock)
-	if gcphase != _GCoff || work.spanSPMCs.all == nil {
+	if gcphase != _GCoff || work.spanSPMCs.list.empty() {
 		unlock(&work.spanSPMCs.lock)
 		return
 	}
-	r := work.spanSPMCs.all
+	r := (*spanSPMC)(work.spanSPMCs.list.head())
 	for r != nil {
-		next := r.allnext
+		next := (*spanSPMC)(unsafe.Pointer(r.allnode.next))
 		if r.dead.Load() {
-			// It's dead. Deinitialize and free it.
-			prev := r.allprev
-			if prev != nil {
-				prev.allnext = next
-			}
-			if next != nil {
-				next.allprev = prev
-			}
-			if work.spanSPMCs.all == r {
-				work.spanSPMCs.all = next
-			}
-
+			// It's dead. Remove, deinitialize and free it.
+			work.spanSPMCs.list.remove(unsafe.Pointer(r))
 			r.deinit()
 			mheap_.spanSPMCAlloc.free(unsafe.Pointer(r))
 		}
diff --git a/src/runtime/mgcmark_nogreenteagc.go b/src/runtime/mgcmark_nogreenteagc.go
index 024565ef3e..a0470c6e32 100644
--- a/src/runtime/mgcmark_nogreenteagc.go
+++ b/src/runtime/mgcmark_nogreenteagc.go
@@ -68,6 +68,7 @@ func (q *spanQueue) destroy() {
 
 type spanSPMC struct {
 	_ sys.NotInHeap
+	allnode listNodeManual
 }
 
 func freeDeadSpanSPMCs() {