[go] runtime: add freeSlice
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t hepudds (Gerrit)
Sep 8, 2025, 1:48:10 PMSep 8
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runtime: add freeSlice
WIP.
This CL is part of a series of CLs to triangulate between the runtime,
compiler, and standard library to reduce how much work the GC must do.
This adds runtime.freeSlice as a convenience function over
runtime.freeSized.
It is exercised in the following CLs in the stack.
Change-Id: Ic116c736b2f84fdce72c44807b036fa0437d9437
Change diff
diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index ea63883..5a3ff87 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -101,6 +101,7 @@
package runtime
import (
+ "internal/abi"
"internal/goarch"
"internal/goexperiment"
"internal/goos"
@@ -2040,6 +2041,41 @@
return true
}
+// freeSlice records that the backing array for a slice is reusable and
+// available for immediate reuse in a subsequent mallocgc allocation.
+// It is a convenience wrapper function over freeSized.
+//
+// sl must contain a pointer to a slice (that is, *[]T). sl is an
+// interface to aid with finding the type.
+//
+// The slice data pointer must point to the base of the heap object (that is,
+// not resliced to the middle of the heap object). See freeSized
+// for additional requirements.
+func freeSlice(sl any) {
+ i := efaceOf(&sl)
+
+ capacity := (*slice)(i.data).cap
+ if capacity == 0 {
+ return
+ }
+
+ // Find the slice element type.
+ typ := (*_type)(abi.NoEscape(unsafe.Pointer(i._type))) // runtime types are never freed
+ if typ.Kind_&abi.KindMask != abi.Pointer {
+ throw("slice result of non-ptr type")
+ }
+ typ = (*ptrtype)(unsafe.Pointer(typ)).Elem
+ if typ.Kind_&abi.KindMask != abi.Slice {
+ throw("slice of non-ptr-to-slice type")
+ }
+ typ = (*slicetype)(unsafe.Pointer(typ)).Elem // slice element type
+
+ // Free the backing array.
+ noscan := !typ.Pointers()
+ freeSized((*slice)(i.data).array, uintptr(capacity)*typ.Size_, noscan)
+ *((*slice)(i.data)) = slice{}
+}
+
// nextReusableNoScan returns the next reusable object for a noscan span,
// or 0 if no reusable object is found.
func (c *mcache) nextReusableNoScan(s *mspan, spc spanClass) (gclinkptr, *mspan) {
@@ -2299,6 +2335,16 @@
return freeSized(p, size, noscan)
}
+//go:linkname slices_freeSized slices.runtimefreesized
+func slices_freeSized(p unsafe.Pointer, size uintptr, noscan bool) bool {
+ return freeSized(p, size, noscan)
+}
+
+//go:linkname slices_freeSlice slices.runtimefreeslice
+func slices_freeSlice(sl any) {
+ freeSlice(sl)
+}
+
// reflect_unsafe_New is meant for package reflect,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
Change information
Files:
- M src/runtime/malloc.go
Change size: S
Delta: 1 file changed, 46 insertions(+), 0 deletions(-)
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t hepudds (Gerrit)
Sep 8, 2025, 9:01:46 PMSep 8
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t hepudds (Gerrit)
Sep 8, 2025, 10:04:06 PMSep 8
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t hepudds (Gerrit)
Sep 8, 2025, 10:05:00 PMSep 8
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t hepudds (Gerrit)
Oct 26, 2025, 9:01:17 PM (10 days ago) Oct 26
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t hepudds (Gerrit)
Oct 27, 2025, 12:09:28 AM (10 days ago) Oct 27
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t hepudds (Gerrit)
Oct 27, 2025, 2:19:50 PM (10 days ago) Oct 27
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t hepudds (Gerrit)
Nov 3, 2025, 6:42:27 PM (2 days ago) Nov 3
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t hepudds (Gerrit)
Nov 3, 2025, 9:03:07 PM (2 days ago) Nov 3
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t hepudds (Gerrit)
Nov 4, 2025, 1:08:39 PM (2 days ago) Nov 4
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