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runtime: SetFinalizer causes undesirable memory overhead #45581

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zhangqiang-01 opened this issue Apr 15, 2021 · 3 comments
Closed

runtime: SetFinalizer causes undesirable memory overhead #45581

zhangqiang-01 opened this issue Apr 15, 2021 · 3 comments

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@zhangqiang-01
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@zhangqiang-01 zhangqiang-01 commented Apr 15, 2021

What version of Go are you using (go version)?

$ go version
go version go1.15.1 linux/amd64

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE="auto"
GOARCH="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/root/gosrc/pkg/mod"
GONOPROXY="code.byted.org"
GONOSUMDB="code.byted.org"
GOOS="linux"
GOPATH="/root/gosrc/"
GOPRIVATE="code.byted.org"
GOPROXY="https://go-mod-proxy.byted.org,https://goproxy.cn,direct"
GOROOT="/root/go"
GOSUMDB="sum.golang.google.cn"
GOTMPDIR=""
GOTOOLDIR="/root/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build392013595=/tmp/go-build -gno-record-gcc-switches"

What did you do?

package main

import (
	"runtime"
	"sync"
	"time"
)

type A struct {
	buf []byte
}

func finalize(a interface{}) {
}

func test(wg *sync.WaitGroup) {
	for i := 0; i < 100000; i++ {
		for j := 0; j < 100000; j++ {

			a := &A{
				buf: make([]byte, 1024*1024),
			}
			runtime.SetFinalizer(a, finalize)

		}
		time.Sleep(time.Microsecond)
	}

	wg.Done()
}

func main() {
	n := 100
	wg := &sync.WaitGroup{}
	wg.Add(n)
	
	for i := 0; i < n; i++ {
		go test(wg)
	}

	wg.Wait()
}

What did you expect to see?

I want the process to consume less memory.

What did you see instead?

Use SetFinalizer:
Actual memory usage 101GB
VmRSS: 106328688 kB

Unuse SetFinalizer:
Actual memory usage 4.5GB
VmRSS: 5481500 kB

@seankhliao seankhliao changed the title runtime.SetFinalizer causes undesirable memory overhead runtime: SetFinalizer causes undesirable memory overhead Apr 15, 2021
@randall77
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@randall77 randall77 commented Apr 15, 2021

I'm presuming that this is because the finalizer thread (which is serial) can't keep up with your testing goroutines (which run in parallel). From the SetFinalizer docs:

A single goroutine runs all finalizers for a program, sequentially.

Does this happen for smaller n?

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@ianlancetaylor
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@ianlancetaylor ianlancetaylor commented Apr 15, 2021

In any case runtime.SetFinalizer is not free. It does take memory to record the fact that a finalizer exists.

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@zhangqiang-01
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@zhangqiang-01 zhangqiang-01 commented Apr 16, 2021

It can only be this way, runtime.SetFinalizer will bring a relatively high budget.

I set n = 10.
Use SetFinalizer:
actual memory usage 9GB。
Unuse SetFinalizer:
actual memory usage 530MB。

I set n = 1
Use SetFinalizer:
actual memory usage 610MB。
Unuse SetFinalizer:
actual memory usage 147MB。

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4 participants