runtime: add ClearSpan experiment to clear spans on first allocation-golang-AtomGit

已合并

runtime: add ClearSpan experiment to clear spans on first allocation #61

cyf_123123创建于 5月13日从qq_44302067/openeuler_golang： clearspan 合入到 openeuler/golang： go1.24.6

runtime: add ClearSpan experiment to clear spans on first allocation #61

已合并

cyf_123123创建于 5月13日

从qq_44302067/openeuler_golang clearspan合入到openeuler/golang go1.24.6

共 6 个文件变更+88-2

Asrc/internal/goexperiment/exp_clearspan_off.go+8-0

@@ -0,0 +1,8 @@
	1	+// Code generated by mkconsts.go. DO NOT EDIT.
	2	+
	3	+//go:build !goexperiment.clearspan
	4	+
	5	+package goexperiment
	6	+
	7	+const ClearSpan = false
	8	+const ClearSpanInt = 0

Asrc/internal/goexperiment/exp_clearspan_on.go+8-0

@@ -0,0 +1,8 @@
	1	+// Code generated by mkconsts.go. DO NOT EDIT.
	2	+
	3	+//go:build goexperiment.clearspan
	4	+
	5	+package goexperiment
	6	+
	7	+const ClearSpan = true
	8	+const ClearSpanInt = 1

Msrc/internal/goexperiment/flags.go+3-0

	@@ -137,4 +137,7 @@ type Flags struct {
137		137
138	// RevertCopyHashKeys enables the "revert" hash map implementation.	138	// RevertCopyHashKeys enables the "revert" hash map implementation.
139	RevertCopyHashKeys bool	139	RevertCopyHashKeys bool
		140	+
		141	+ // Clear the span if necessary
		142	+ ClearSpan bool
140	}	143	}

Asrc/runtime/clearspan_test.go+19-0

@@ -0,0 +1,19 @@
	1	+// Copyright (c) Huawei Technologies Co., Ltd. 2025-2025. All rights reserved.
	2	+package runtime_test
	3	+
	4	+import (
	5	+ "internal/goexperiment"
	6	+ "runtime"
	7	+ "testing"
	8	+)
	9	+
	10	+func TestClearSpan(t *testing.T) {
	11	+ needzero, cleared := runtime.TryClearSpanFunc()
	12	+ if goexperiment.ClearSpan {
	13	+ if needzero != 0 \|\| !cleared {
	14	+ t.Fatalf("ClearSpan enabled: expected needzero=0 and cleared=true, got needzero=%d cleared=%v", needzero, cleared)
	15	+ }
	16	+ } else if needzero == 0 \|\| cleared {
	17	+ t.Fatalf("ClearSpan disabled: expected needzero!=0 and cleared=false, got needzero=%d cleared=%v", needzero, cleared)
	18	+ }
	19	+}

Asrc/runtime/export_runtime_test.go+35-0

@@ -0,0 +1,35 @@
	1	+// Copyright (c) Huawei Technologies Co., Ltd. 2025-2025. All rights reserved.
	2	+
	3	+package runtime
	4	+
	5	+import "unsafe"
	6	+
	7	+func TryClearSpanFunc() (needzero uint8, cleared bool) {
	8	+ buf := make([]byte, 128)
	9	+ for i := range buf {
	10	+ buf[i] = 0xff
	11	+ }
	12	+
	13	+ ms := AllocMSpan()
	14	+ defer FreeMSpan(ms)
	15	+
	16	+ s := (*mspan)(unsafe.Pointer(ms))
	17	+ s.startAddr = uintptr(unsafe.Pointer(&buf[0]))
	18	+ s.elemsize = 16
	19	+ s.nelems = uint16(len(buf) / int(s.elemsize))
	20	+ s.allocCount = 0
	21	+ s.needzero = 1
	22	+
	23	+ clearSpanFunc(s)
	24	+
	25	+ needzero = s.needzero
	26	+ cleared = true
	27	+ for _, b := range buf {
	28	+ if b != 0 {
	29	+ cleared = false
	30	+ break
	31	+ }
	32	+ }
	33	+ KeepAlive(buf)
	34	+ return
	atomgit-bot5月14日 🟡 Medium Priority TryClearSpanFunc 通过 allocmcache() 获取 mcache，其 alloc[spc] 指向全局 emptymspan（见 mcache.go:95 初始化逻辑）。测试直接修改 emptymspan.needzero 并对其调用 clearSpanFunc，这会触发 memclrNoHeapPointers(unsafe.Pointer(0), 0)。虽然各平台 memclrNoHeapPointers 实现对 size=0 均安全返回，但修改全局 emptymspan 破坏了测试隔离性，并行测试下可能触发 race detector 报警，且 emptymspan.needzero 被永久修改可能影响后续依赖该值的逻辑。同一段代码其他问题 `导出的变量 Class_to_size / Size_to_class8 / Size_to_class128 未被使用`：这三个变量在该文件及整个 diff 范围内均未被任何测试引用，属于无用的导出，增加维护负担并可被误认为有外部依赖。不准确？ cyf_123123 5月18日评论： 5月18日评论：
	35	+}

Msrc/runtime/malloc.go+15-2

	@@ -102,6 +102,7 @@ package runtime
102		102
103	import (	103	import (
104	"internal/goarch"	104	"internal/goarch"
		105	+ "internal/goexperiment"
105	"internal/goos"	106	"internal/goos"
106	"internal/runtime/atomic"	107	"internal/runtime/atomic"
107	"internal/runtime/math"	108	"internal/runtime/math"
	@@ -972,6 +973,9 @@ func (c mcache) nextFree(spc spanClass) (v gclinkptr, s mspan, checkGCTrigger
972	throw("freeIndex is not valid")	973	throw("freeIndex is not valid")
973	}	974	}
974		975
		976	+ // Clear the span if necessary
		977	+ clearSpanFunc(s)
		978	+
975	v = gclinkptr(uintptr(freeIndex)*s.elemsize + s.base())	979	v = gclinkptr(uintptr(freeIndex)*s.elemsize + s.base())
976	s.allocCount++	980	s.allocCount++
977	if s.allocCount > s.nelems {	981	if s.allocCount > s.nelems {
	@@ -981,6 +985,13 @@ func (c mcache) nextFree(spc spanClass) (v gclinkptr, s mspan, checkGCTrigger
981	return	985	return
982	}	986	}
983		987
		988	+func clearSpanFunc(s *mspan) {
		989	+ if goexperiment.ClearSpan && (s.allocCount == 0) && (s.needzero != 0) {
		990	+ memclrNoHeapPointers(unsafe.Pointer(s.startAddr), (s.elemsize * uintptr(s.nelems)))
		991	+ s.needzero = 0
		992	+ }
		993	+}
		994	+
984	// doubleCheckMalloc enables a bunch of extra checks to malloc to double-check	995	// doubleCheckMalloc enables a bunch of extra checks to malloc to double-check
985	// that various invariants are upheld.	996	// that various invariants are upheld.
986	//	997	//
	@@ -1175,8 +1186,10 @@ func mallocgcTiny(size uintptr, typ *_type, needzero bool) (unsafe.Pointer, uint
1175	v, span, checkGCTrigger = c.nextFree(tinySpanClass)	1186	v, span, checkGCTrigger = c.nextFree(tinySpanClass)
1176	}	1187	}
1177	x := unsafe.Pointer(v)	1188	x := unsafe.Pointer(v)
1178	- (*[2]uint64)(x)[0] = 0	1189	+ if !goexperiment.ClearSpan \|\| span.needzero != 0 {
1179	- (*[2]uint64)(x)[1] = 0	1190	+ (*[2]uint64)(x)[0] = 0
		1191	+ (*[2]uint64)(x)[1] = 0
		1192	+ }
1180	// See if we need to replace the existing tiny block with the new one	1193	// See if we need to replace the existing tiny block with the new one
1181	// based on amount of remaining free space.	1194	// based on amount of remaining free space.
1182	if !raceenabled && (size < c.tinyoffset \|\| c.tiny == 0) {	1195	if !raceenabled && (size < c.tinyoffset \|\| c.tiny == 0) {