linux - 如何减少gccgo编译的可执行文件所需的虚拟内存？

当我使用gccgo编译这个简单的hello world示例时，生成的可执行文件使用了超过800 MiB的VmData。我想知道为什么，如果有什么我可以降低的。睡眠只是让我有时间观察内存使用情况。

来源:

package main

import (
  "fmt"
  "time"
)

func main() {
  fmt.Println("hello world")
  time.Sleep(1000000000 * 5)
}

我用来编译的脚本:

#!/bin/bash

TOOLCHAIN_PREFIX=i686-linux-gnu
OPTIMIZATION_FLAG="-O3"

CGO_ENABLED=1 \
CC=${TOOLCHAIN_PREFIX}-gcc-8 \
CXX=${TOOLCHAIN_PREFIX}-g++-8 \
AR=${TOOLCHAIN_PREFIX}-ar \
GCCGO=${TOOLCHAIN_PREFIX}-gccgo-8 \
CGO_CFLAGS="-g ${OPTIMIZATION_FLAG}" \
CGO_CPPFLAGS="" \
CGO_CXXFLAGS="-g ${OPTIMIZATION_FLAG}" \
CGO_FFLAGS="-g ${OPTIMIZATION_FLAG}" \
CGO_LDFLAGS="-g ${OPTIMIZATION_FLAG}" \
GOOS=linux \
GOARCH=386 \
go build -x \
   -compiler=gccgo \
   -gccgoflags=all="-static -g ${OPTIMIZATION_FLAG}" \
   $1

gccgo的版本:

$ i686-linux-gnu-gccgo-8 --version
i686-linux-gnu-gccgo-8 (Ubuntu 8.2.0-1ubuntu2~18.04) 8.2.0
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

/ proc / / status的输出:

VmPeak:  811692 kB
VmSize:  811692 kB
VmLck:        0 kB
VmPin:        0 kB
VmHWM:     5796 kB
VmRSS:     5796 kB
VmData:  807196 kB
VmStk:      132 kB
VmExe:     2936 kB
VmLib:        0 kB
VmPTE:       52 kB
VmPMD:        0 kB
VmSwap:       0 kB

我问是因为我的设备只有512 MiB的RAM。我知道这是虚拟内存，但我想尽可能减少或删除过量使用。对于我来说，一个简单的可执行文件需要这么多分配似乎并不合理。

最佳答案

我能够找到gccgo要求这么多内存的位置。它在mallocinit函数的libgo / go / runtime / malloc.go文件中:

// If we fail to allocate, try again with a smaller arena.
// This is necessary on Android L where we share a process
// with ART, which reserves virtual memory aggressively.
// In the worst case, fall back to a 0-sized initial arena,
// in the hope that subsequent reservations will succeed.
arenaSizes := [...]uintptr{
  512 << 20,
  256 << 20,
  128 << 20,
  0,
}

for _, arenaSize := range &arenaSizes {
  // SysReserve treats the address we ask for, end, as a hint,
  // not as an absolute requirement. If we ask for the end
  // of the data segment but the operating system requires
  // a little more space before we can start allocating, it will
  // give out a slightly higher pointer. Except QEMU, which
  // is buggy, as usual: it won't adjust the pointer upward.
  // So adjust it upward a little bit ourselves: 1/4 MB to get
  // away from the running binary image and then round up
  // to a MB boundary.
  p = round(getEnd()+(1<<18), 1<<20)
  pSize = bitmapSize + spansSize + arenaSize + _PageSize
  if p <= procBrk && procBrk < p+pSize {
    // Move the start above the brk,
    // leaving some room for future brk
    // expansion.
    p = round(procBrk+(1<<20), 1<<20)
  }
  p = uintptr(sysReserve(unsafe.Pointer(p), pSize, &reserved))
  if p != 0 {
    break
  }
}
if p == 0 {
  throw("runtime: cannot reserve arena virtual address space")
}

有趣的是，如果较大的失败，它将退回到较小的竞技场。因此，限制可用于go可执行文件的虚拟内存实际上将限制它成功分配的内存量。

我能够使用ulimit -v 327680将虚拟内存限制为较小的数字:

VmPeak:   300772 kB
VmSize:   300772 kB
VmLck:         0 kB
VmPin:         0 kB
VmHWM:      5712 kB
VmRSS:      5712 kB
VmData:   296276 kB
VmStk:       132 kB
VmExe:      2936 kB
VmLib:         0 kB
VmPTE:        56 kB
VmPMD:         0 kB
VmSwap:        0 kB

这些仍然是很大的数字，但是gccgo可执行文件可以达到的最好效果。因此，问题的答案是，是的，您可以减少gccgo编译的可执行文件的VmData，但您实际上不必为此担心。 (在64位计算机上，gccgo尝试分配512 GB。)