From 53009b26dd2e8b75fba8b44849e1d323ddb2a31f Mon Sep 17 00:00:00 2001 From: Cherry Mui Date: Sun, 22 Jun 2025 15:40:02 -0400 Subject: runtime: use a smaller arena size on Wasm On Wasm, some programs have very small heap. Currently, we use 4 MB arena size (like all other 32-bit platforms). For a very small program, it needs to allocate one heap arena, 4 MB size at a 4 MB aligned address. So we'll need 8 MB of linear memory, whereas only a smaller portion is actually used by the program. On Wasm, samll programs are not uncommon (e.g. WASI plugins), and users are concerned about the memory usage. This CL switches to a smaller arena size, as well as a smaller page allocator chunk size (both are now 512 KB). So the heap will be grown in 512 KB granularity. For a helloworld program, it now uses less than 3 MB of linear memory, instead of 8 MB. Change-Id: Ibd66c1fa6e794a12c00906cbacc8f2e410f196c4 Reviewed-on: https://go-review.googlesource.com/c/go/+/683296 Reviewed-by: David Chase Reviewed-by: Michael Knyszek LUCI-TryBot-Result: Go LUCI --- src/runtime/malloc.go | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) (limited to 'src/runtime/malloc.go') diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go index db91e89359..fc4f21b532 100644 --- a/src/runtime/malloc.go +++ b/src/runtime/malloc.go @@ -233,19 +233,22 @@ const ( // ios/arm64 40 4MB 1 256K (2MB) // */32-bit 32 4MB 1 1024 (4KB) // */mips(le) 31 4MB 1 512 (2KB) + // wasm 32 512KB 1 8192 (64KB) // heapArenaBytes is the size of a heap arena. The heap // consists of mappings of size heapArenaBytes, aligned to // heapArenaBytes. The initial heap mapping is one arena. // - // This is currently 64MB on 64-bit non-Windows and 4MB on - // 32-bit and on Windows. We use smaller arenas on Windows - // because all committed memory is charged to the process, - // even if it's not touched. Hence, for processes with small - // heaps, the mapped arena space needs to be commensurate. - // This is particularly important with the race detector, - // since it significantly amplifies the cost of committed - // memory. + // This is currently 64MB on 64-bit non-Windows, 4MB on + // 32-bit and on Windows, and 512KB on Wasm. We use smaller + // arenas on Windows because all committed memory is charged + // to the process, even if it's not touched. Hence, for + // processes with small heaps, the mapped arena space needs + // to be commensurate. This is particularly important with + // the race detector, since it significantly amplifies the + // cost of committed memory. We use smaller arenas on Wasm + // because some Wasm programs have very small heap, and + // everything in the Wasm linear memory is charged. heapArenaBytes = 1 << logHeapArenaBytes heapArenaWords = heapArenaBytes / goarch.PtrSize @@ -253,7 +256,7 @@ const ( // logHeapArenaBytes is log_2 of heapArenaBytes. For clarity, // prefer using heapArenaBytes where possible (we need the // constant to compute some other constants). - logHeapArenaBytes = (6+20)*(_64bit*(1-goos.IsWindows)*(1-goarch.IsWasm)*(1-goos.IsIos*goarch.IsArm64)) + (2+20)*(_64bit*goos.IsWindows) + (2+20)*(1-_64bit) + (2+20)*goarch.IsWasm + (2+20)*goos.IsIos*goarch.IsArm64 + logHeapArenaBytes = (6+20)*(_64bit*(1-goos.IsWindows)*(1-goarch.IsWasm)*(1-goos.IsIos*goarch.IsArm64)) + (2+20)*(_64bit*goos.IsWindows) + (2+20)*(1-_64bit) + (9+10)*goarch.IsWasm + (2+20)*goos.IsIos*goarch.IsArm64 // heapArenaBitmapWords is the size of each heap arena's bitmap in uintptrs. heapArenaBitmapWords = heapArenaWords / (8 * goarch.PtrSize) -- cgit v1.3-5-g9baa