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处理不受setrlimit限制的资源

setrlimit ulimit malloc memory-management c

pa1 · 技术社区 · 9 年前

我编写了一个简单的程序,将它的数据大小限制在65Kb,并验证了这一点。我正在分配一个大于65Kb的虚拟内存,如果我做得正确(如下所示),逻辑上malloc调用应该失败,不是吗?

#include <sys/resource.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

int main (int argc, char *argv[])
{
  struct rlimit limit;


  /* Get max data size . */
  if (getrlimit(RLIMIT_DATA, &limit) != 0) {
    printf("getrlimit() failed with errno=%d\n", errno);
    return 1;
  }

  printf("The soft limit is %lu\n", limit.rlim_cur);
  printf("The hard limit is %lu\n", limit.rlim_max);

  limit.rlim_cur = 65 * 1024;
  limit.rlim_max = 65 * 1024;

  if (setrlimit(RLIMIT_DATA, &limit) != 0) {
    printf("setrlimit() failed with errno=%d\n", errno);
    return 1;
  }

  if (getrlimit(RLIMIT_DATA, &limit) != 0) {
    printf("getrlimit() failed with errno=%d\n", errno);
    return 1;
  }

  printf("The soft limit is %lu\n", limit.rlim_cur);
  printf("The hard limit is %lu\n", limit.rlim_max);
  system("bash -c 'ulimit -a'");
    int *new2 = NULL;
    new2 = malloc(66666666);
    if (new2 == NULL)
    {
        printf("malloc failed\n");
        return;
    }
    else
    {
        printf("success\n");
    }

  return 0;
}

令人惊讶的是,输出是这样的-

The soft limit is 4294967295
The hard limit is 4294967295
The soft limit is 66560
The hard limit is 66560
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) 65
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 14895
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 14895
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited
success

我做错了吗? 请放弃您的输入。谢谢

2 回复 | 直到 9 年前

kaylum 9 年前

从 setrlimit man page :

RLIMIT_数据

进程数据段的最大大小(已初始化数据、未初始化数据和堆)。此限制影响呼叫到brk(2)和sbrk(2),它们失败,错误为ENOMEM 遇到此资源的软限制。

具体来说,该资源不适用于通过 mmap .内部 malloc 使用各种机制来获得新的存储器。在这种情况下,您会发现它使用 mmap公司 而不是 sbrk 或 brk 。您可以通过使用转储程序中的系统调用来验证这一点 strace .

要实现您的目标,请使用 RLIMIT_AS 资源。

user3629249 9 年前

在纠正代码编译的问题之后。

这是代码:

#include <sys/resource.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

int main ( void )
{
  struct rlimit limit;


  /* Get max data size . */
  if (getrlimit(RLIMIT_DATA, &limit) != 0) {
    printf("getrlimit() failed with errno=%d\n", errno);
    exit( EXIT_FAILURE );
  }

  printf("The soft limit is %lu\n", limit.rlim_cur);
  printf("The hard limit is %lu\n", limit.rlim_max);

  limit.rlim_cur = 65 * 1024;
  limit.rlim_max = 65 * 1024;

  if (setrlimit(RLIMIT_DATA, &limit) != 0)
  {
    printf("setrlimit() failed with errno=%d\n", errno);
    exit( EXIT_FAILURE );
  }

  if (getrlimit(RLIMIT_DATA, &limit) != 0)
  {
    printf("getrlimit() failed with errno=%d\n", errno);
    exit( EXIT_FAILURE );
  }

  printf("The soft limit is %lu\n", limit.rlim_cur);
  printf("The hard limit is %lu\n", limit.rlim_max);
  system("bash -c 'ulimit -a'");

    int *new2 = NULL;
    new2 = malloc(66666666);

    if (new2 == NULL)
    {
        printf("malloc failed\n");
        exit( EXIT_FAILURE );
    }
    else
    {
        printf("success\n");
    }

  return 0;
}

这里是输出:

The soft limit is 18446744073709551615
The hard limit is 18446744073709551615
The soft limit is 66560
The hard limit is 66560
bash: xmalloc: .././variables.c:2307: cannot allocate 48 bytes (16384 bytes allocated)
success

这表示对rlimit的修改有效 system 呼叫成功 bash 命令失败 malloc 成功。

多次运行同一代码总是输出完全相同的值,因此rlimit值不会发生永久性更改

在运行上述代码几次后,保持每个终端窗口打开,然后运行 猛击 另一个终端窗口中的命令导致以下结果:

core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 54511
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 54511
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

然后在另一个终端中运行代码,然后运行 猛击 命令在同一终端输出完全相同的输出值。

因此,我怀疑代码采取了错误的方法来限制可用的内存量。