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x/crypto/scrypt: memory not released after hash is calculated #20000

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awnumar opened this issue Apr 16, 2017 · 1 comment
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x/crypto/scrypt: memory not released after hash is calculated #20000

awnumar opened this issue Apr 16, 2017 · 1 comment
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@awnumar
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awnumar commented Apr 16, 2017 •
edited

What version of Go are you using?

go version go1.8.1 linux/amd64

What operating system and processor architecture are you using?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/awn/go"
GORACE=""
GOROOT="/usr/lib/go"
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build015290357=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

package main

import (
	"fmt"
	"time"

	"golang.org/x/crypto/scrypt"
)

func main() {
	key, _ := scrypt.Key(
		[]byte(""), // Input data.
		[]byte(""), // Salt.
		1<<18,      // Scrypt parameter N.
		16,         // Scrypt parameter r.
		1,          // Scrypt parameter p.
		64)         // Output hash length.

	fmt.Println(key)

	// Keep the process running.
	time.Sleep(10 * time.Second)
}

What did you expect to see?

I expected to see the memory usage drop back down after the hash was calculated and the result was returned to the caller.

What did you see instead?

I saw the memory usage stay at the peak usage until the process terminated.

screenshot from 2017-04-16 16-00-48

This leads to a lot of problems if the Scrypt parameters are high and Scrypt is called multiple times (not an unlikely scenario).
@bradfitz
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This is normal. It'll be returned to the operating system eventually (by the Go scavenger), if it's not reused by Go before then.

See https://golang.org/pkg/runtime/debug/#FreeOSMemory

@golang golang locked and limited conversation to collaborators Apr 16, 2018
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@bradfitz @gopherbot @awnumar