Re: [PATCH] Prevent OOM from killing init

[Jonathan Morton]

>The main point is letting malloc fail when the memory cannot be
>guaranteed.

If I read various things correctly, malloc() is supposed to fail as you
would expect if /proc/sys/vm/overcommit_memory is 0.  This is the case on
my RH 6.2 box, dunno about yours.  I can write a simple test program which
simply allocates tons of memory if you like...

...and I did.  It filled up my physical and swap memory, and got killed by
the OOM handler before malloc() failed, even though overcommit_memory was
set to 0.

*****BAD!*****

Here's my test program and output (on a Duron with 256M physical and 250M
swap):

[chromi@beryllium compsci]$ cat make_mem.c
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  /* Allocate tons of RAM, print out how far, we get, and exit when we
malloc() fails.
   * We also access each page we allocate, to ensure we really are getting
the memory we reserve.
   * If we are killed by SIGSEGV or by OOM instead of malloc() failing, the
VM system is broken.
   */

  char *p;
  unsigned long pages = 0;

  while(1) {
    p = malloc(1024);
    if(!p)
      break;
    *p = 1;
    pages++;
    printf("%lu K\r", pages);
  }

  printf("\n*** malloc() failed!\n");

  return 0;
}
[chromi@beryllium compsci]$ gcc -O -Wall -o make_mem make_mem.c
[chromi@beryllium compsci]$ ./make_mem
493625 KKilled
[chromi@beryllium compsci]$

--------------------------------------------------------------
from:     Jonathan "Chromatix" Morton
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