How to set memory limit to a process in Golang

Issue

I use syscall prlimit to set resource limit to process, it works for limit CPU time but when test memory usage, I come with the problem.

package sandbox

import (
    "syscall"
    "unsafe"
)

func prLimit(pid int, limit uintptr, rlimit *syscall.Rlimit) error {
    _, _, errno := syscall.RawSyscall6(syscall.SYS_PRLIMIT64, uintptr(pid), limit, uintptr(unsafe.Pointer(rlimit)), 0, 0, 0)
    var err error
    if errno != 0 {
        err = errno
        return err
    } else {
        return nil
    }
}

and it’s my test.

func TestMemoryLimit(t *testing.T) {
    proc, err := os.StartProcess("test/memo", []string{"memo"}, &os.ProcAttr{})
    if err != nil {
        panic(err)
    }
    defer proc.Kill()
    var rlimit syscall.Rlimit
    rlimit.Cur = 10
    rlimit.Max = 10 + 1024
    prLimit(proc.Pid, syscall.RLIMIT_DATA, &rlimit)
    status, err := proc.Wait()
    if status.Success() {
        t.Fatal("memory test failed")
    }
}

this is memo:

package main

func main() {
    var a [10000][]int
    for i := 0; i < 1000; i++ {
        a[i] = make([]int, 1024)
    }
}

I make a large amount of memory and set only 10 bytes for the memory , but it won’t signal segment fault signal any way.

Solution

RLIMIT_DATA describes the maximum size of a processes data segment. Traditionally, programs that allocate memory enlarge the data segment with calls to brk() to allocate memory from the operating system.

Go doesn’t use this approach. Instead, it uses a variant of the mmap() system call to request regions of memory anywhere in the address space. This is much more flexible than a brk() based approach as you can deallocate arbitrary memory regions with munmap(), whereas a brk() based approach can only deallocate memory from the end of the data segment.

The result of this is that RLIMIT_DATA is inneffective in controlling the amount of memory a process uses. Try using RLIMIT_AS instead, but beware that this limit also incorporates the address space you use for file mappings, especially in the case of shared libraries.

Answered By – fuz

Answer Checked By – Mildred Charles (GoLangFix Admin)

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