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runtime, cmd/link: optimize memory allocation on wasm

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WebAssembly's memory is contiguous. Allocating memory at a high address
also allocates all memory up to that address. This change reduces
the initial memory allocated on wasm from 1GB to 16MB by using multiple
heap arenas and reducing the size of a heap arena.

Fixes #27462.

Change-Id: Ic941e6edcadd411e65a14cb2f9fd6c8eae02fc7a
Reviewed-on: https://go-review.googlesource.com/c/go/+/170950
Run-TryBot: Richard Musiol <neelance@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Richard Musiol 2019-04-08 00:36:55 +02:00 • committed by Richard Musiol
parent e47090ab40
commit 460f9c6068
2 changed files with 11 additions and 11 deletions
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18
src/cmd/link/internal/wasm/asm.go
View file

@ -297,18 +297,18 @@ func writeTableSec(ctxt *ld.Link, fns []*wasmFunc) {
}
// writeMemorySec writes the section that declares linear memories. Currently one linear memory is being used.
// Linear memory always starts at address zero. More memory can be requested with the GrowMemory instruction.
func writeMemorySec(ctxt *ld.Link) {
sizeOffset := writeSecHeader(ctxt, sectionMemory)
// Linear memory always starts at address zero.
// The unit of the sizes is "WebAssembly page size", which is 64Ki.
// The minimum is currently set to 1GB, which is a lot.
// More memory can be requested with the grow_memory instruction,
// but this operation currently is rather slow, so we avoid it for now.
// TODO(neelance): Use lower initial memory size.
writeUleb128(ctxt.Out, 1) // number of memories
ctxt.Out.WriteByte(0x00) // no maximum memory size
writeUleb128(ctxt.Out, 1024*16) // minimum (initial) memory size
const (
initialSize = 16 << 20 // 16MB, enough for runtime init without growing
wasmPageSize = 64 << 10 // 64KB
)
writeUleb128(ctxt.Out, 1) // number of memories
ctxt.Out.WriteByte(0x00) // no maximum memory size
writeUleb128(ctxt.Out, initialSize/wasmPageSize) // minimum (initial) memory size
writeSecSize(ctxt, sizeOffset)
}