runtime: support runtime.freegc in size-specialized mallocs for noscan objects

This CL is part of a set of CLs that attempt to reduce how much work the
GC must do. See the design in https://go.dev/design/74299-runtime-freegc

This CL updates the smallNoScanStub stub in malloc_stubs.go to reuse
heap objects that have been freed by runtime.freegc calls, and generates
the corresponding size-specialized code in malloc_generated.go.

This CL only adds support in the specialized mallocs for noscan
heap objects (objects without pointers). A later CL handles objects
with pointers.

While we are here, we leave a couple of breadcrumbs in mkmalloc.go on
how to do the generation.

Updates #74299

Change-Id: I2657622601a27211554ee862fce057e101767a70
Reviewed-on: https://go-review.googlesource.com/c/go/+/715761
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

src/runtime/_mkmalloc/mkmalloc.go

@@ -254,7 +254,8 @@ func inline(config generatorConfig) []byte {
 	}
 
 	// Write out the package and import declarations.
-	out.WriteString("// Code generated by mkmalloc.go; DO NOT EDIT.\n\n")
+	out.WriteString("// Code generated by mkmalloc.go; DO NOT EDIT.\n")
+	out.WriteString("// See overview in malloc_stubs.go.\n\n")
 	out.WriteString("package " + f.Name.Name + "\n\n")
 	for _, importDecl := range importDecls {
 		out.Write(mustFormatNode(fset, importDecl))

src/runtime/malloc.go

@@ -1094,6 +1094,8 @@ const sizeSpecializedMallocEnabled = goexperiment.SizeSpecializedMalloc && GOOS
 // implementation and the corresponding allocation-related changes: the experiment must be
 // enabled, and none of the memory sanitizers should be enabled. We allow the race detector,
 // in contrast to sizeSpecializedMallocEnabled.
+// TODO(thepudds): it would be nice to check Valgrind integration, though there are some hints
+// there might not be any canned tests in tree for Go's integration with Valgrind.
 const runtimeFreegcEnabled = goexperiment.RuntimeFreegc && !asanenabled && !msanenabled && !valgrindenabled
 
 // Allocate an object of size bytes.
@@ -1966,10 +1968,15 @@ const (
 // or roughly when the liveness analysis of the compiler
 // would otherwise have determined ptr's object is reclaimable by the GC.
 func freegc(ptr unsafe.Pointer, size uintptr, noscan bool) bool {
-	if !runtimeFreegcEnabled || sizeSpecializedMallocEnabled || !reusableSize(size) {
+	if !runtimeFreegcEnabled || !reusableSize(size) {
-		// TODO(thepudds): temporarily disable freegc with SizeSpecializedMalloc until we finish integrating.
 		return false
 	}
+	if sizeSpecializedMallocEnabled && !noscan {
+		// TODO(thepudds): temporarily disable freegc with SizeSpecializedMalloc for pointer types
+		// until we finish integrating.
+		return false
+	}
+
 	if ptr == nil {
 		throw("freegc nil")
 	}

src/runtime/malloc_generated.go

@@ -1,4 +1,5 @@
 // Code generated by mkmalloc.go; DO NOT EDIT.
+// See overview in malloc_stubs.go.
 
 package runtime
 
@@ -6400,6 +6401,32 @@ func mallocgcSmallNoScanSC2(size uintptr, typ *_type, needzero bool) unsafe.Poin
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -6497,6 +6524,32 @@ func mallocgcSmallNoScanSC3(size uintptr, typ *_type, needzero bool) unsafe.Poin
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -6594,6 +6647,32 @@ func mallocgcSmallNoScanSC4(size uintptr, typ *_type, needzero bool) unsafe.Poin
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -6691,6 +6770,32 @@ func mallocgcSmallNoScanSC5(size uintptr, typ *_type, needzero bool) unsafe.Poin
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -6788,6 +6893,32 @@ func mallocgcSmallNoScanSC6(size uintptr, typ *_type, needzero bool) unsafe.Poin
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -6885,6 +7016,32 @@ func mallocgcSmallNoScanSC7(size uintptr, typ *_type, needzero bool) unsafe.Poin
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -6982,6 +7139,32 @@ func mallocgcSmallNoScanSC8(size uintptr, typ *_type, needzero bool) unsafe.Poin
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -7079,6 +7262,32 @@ func mallocgcSmallNoScanSC9(size uintptr, typ *_type, needzero bool) unsafe.Poin
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -7176,6 +7385,32 @@ func mallocgcSmallNoScanSC10(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -7273,6 +7508,32 @@ func mallocgcSmallNoScanSC11(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -7370,6 +7631,32 @@ func mallocgcSmallNoScanSC12(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -7467,6 +7754,32 @@ func mallocgcSmallNoScanSC13(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -7564,6 +7877,32 @@ func mallocgcSmallNoScanSC14(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -7661,6 +8000,32 @@ func mallocgcSmallNoScanSC15(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -7758,6 +8123,32 @@ func mallocgcSmallNoScanSC16(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -7855,6 +8246,32 @@ func mallocgcSmallNoScanSC17(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -7952,6 +8369,32 @@ func mallocgcSmallNoScanSC18(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -8049,6 +8492,32 @@ func mallocgcSmallNoScanSC19(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -8146,6 +8615,32 @@ func mallocgcSmallNoScanSC20(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -8243,6 +8738,32 @@ func mallocgcSmallNoScanSC21(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -8340,6 +8861,32 @@ func mallocgcSmallNoScanSC22(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -8437,6 +8984,32 @@ func mallocgcSmallNoScanSC23(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -8534,6 +9107,32 @@ func mallocgcSmallNoScanSC24(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -8631,6 +9230,32 @@ func mallocgcSmallNoScanSC25(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)
@@ -8728,6 +9353,32 @@ func mallocgcSmallNoScanSC26(size uintptr, typ *_type, needzero bool) unsafe.Poi
 	const spc = spanClass(sizeclass<<1) | spanClass(1)
 	span := c.alloc[spc]
 
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+		x := v
+		{
+
+			if valgrindenabled {
+				valgrindMalloc(x, size)
+			}
+
+			if gcBlackenEnabled != 0 && elemsize != 0 {
+				if assistG := getg().m.curg; assistG != nil {
+					assistG.gcAssistBytes -= int64(elemsize - size)
+				}
+			}
+
+			if debug.malloc {
+				postMallocgcDebug(x, elemsize, typ)
+			}
+			return x
+		}
+
+	}
+
 	var nextFreeFastResult gclinkptr
 	if span.allocCache != 0 {
 		theBit := sys.TrailingZeros64(span.allocCache)

src/runtime/malloc_stubs.go

@@ -7,6 +7,8 @@
 // to produce a full mallocgc function that's specialized for a span class
 // or specific size in the case of the tiny allocator.
 //
+// To generate the specialized mallocgc functions, do 'go run .' inside runtime/_mkmalloc.
+//
 // To assemble a mallocgc function, the mallocStub function is cloned, and the call to
 // inlinedMalloc is replaced with the inlined body of smallScanNoHeaderStub,
 // smallNoScanStub or tinyStub, depending on the parameters being specialized.
@@ -71,7 +73,8 @@ func mallocStub(size uintptr, typ *_type, needzero bool) unsafe.Pointer {
 		}
 	}
 
-	// Assist the GC if needed.
+	// Assist the GC if needed. (On the reuse path, we currently compensate for this;
+	// changes here might require changes there.)
 	if gcBlackenEnabled != 0 {
 		deductAssistCredit(size)
 	}
@@ -242,6 +245,23 @@ func smallNoScanStub(size uintptr, typ *_type, needzero bool) (unsafe.Pointer, u
 	c := getMCache(mp)
 	const spc = spanClass(sizeclass<<1) | spanClass(noscanint_)
 	span := c.alloc[spc]
+
+	// First, check for a reusable object.
+	if runtimeFreegcEnabled && c.hasReusableNoscan(spc) {
+		// We have a reusable object, use it.
+		v := mallocgcSmallNoscanReuse(c, span, spc, elemsize, needzero)
+		mp.mallocing = 0
+		releasem(mp)
+
+		// TODO(thepudds): note that the generated return path is essentially duplicated
+		// by the generator. For example, see the two postMallocgcDebug calls and
+		// related duplicated code on the return path currently in the generated
+		// mallocgcSmallNoScanSC2 function. One set of those correspond to this
+		// return here. We might be able to de-duplicate the generated return path
+		// by updating the generator, perhaps by jumping to a shared return or similar.
+		return v, elemsize
+	}
+
 	v := nextFreeFastStub(span)
 	if v == 0 {
 		v, span, checkGCTrigger = c.nextFree(spc)

src/runtime/malloc_test.go

@@ -349,8 +349,10 @@ func testFreegc[T comparable](noscan bool) func(*testing.T) {
 		t.Run("allocs-with-free", func(t *testing.T) {
 			// Same allocations, but now using explicit free so that
 			// no allocs get reported. (Again, not the desired long-term behavior).
-			if SizeSpecializedMallocEnabled {
+			if SizeSpecializedMallocEnabled && !noscan {
-				t.Skip("temporarily skipping alloc tests for GOEXPERIMENT=sizespecializedmalloc")
+				// TODO(thepudds): skip at this point in the stack for size-specialized malloc
+				// with !noscan. Additional integration with sizespecializedmalloc is in a later CL.
+				t.Skip("temporarily skipping alloc tests for GOEXPERIMENT=sizespecializedmalloc for pointer types")
 			}
 			if !RuntimeFreegcEnabled {
 				t.Skip("skipping alloc tests with runtime.freegc disabled")
@@ -370,8 +372,10 @@ func testFreegc[T comparable](noscan bool) func(*testing.T) {
 			// Multiple allocations outstanding before explicitly freeing,
 			// but still within the limit of our smallest free list size
 			// so that no allocs are reported. (Again, not long-term behavior).
-			if SizeSpecializedMallocEnabled {
+			if SizeSpecializedMallocEnabled && !noscan {
-				t.Skip("temporarily skipping alloc tests for GOEXPERIMENT=sizespecializedmalloc")
+				// TODO(thepudds): skip at this point in the stack for size-specialized malloc
+				// with !noscan. Additional integration with sizespecializedmalloc is in a later CL.
+				t.Skip("temporarily skipping alloc tests for GOEXPERIMENT=sizespecializedmalloc for pointer types")
 			}
 			if !RuntimeFreegcEnabled {
 				t.Skip("skipping alloc tests with runtime.freegc disabled")
@@ -514,10 +518,10 @@ func testFreegc[T comparable](noscan bool) func(*testing.T) {
 			// See https://go.dev/cl/717520 for some additional discussion,
 			// including how we can deliberately cause the test to fail currently
 			// if we purposefully introduce some assist credit bugs.
-			if SizeSpecializedMallocEnabled {
+			if SizeSpecializedMallocEnabled && !noscan {
 				// TODO(thepudds): skip this test at this point in the stack; later CL has
 				// integration with sizespecializedmalloc.
-				t.Skip("temporarily skip assist credit test for GOEXPERIMENT=sizespecializedmalloc")
+				t.Skip("temporarily skip assist credit tests for GOEXPERIMENT=sizespecializedmalloc for pointer types")
 			}
 			if !RuntimeFreegcEnabled {
 				t.Skip("skipping assist credit test with runtime.freegc disabled")