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From: Martin Egholm Nielsen <martin@egholm-nielsen.dk>
Subject: Overcommit problem on embedded device with no swap
Date: Fri, 18 Mar 2005 11:29:42 +0100
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Hi there,

I don't know if this is the right place to go with this problem, but 
having searched the web, I ended up here... Sorry if this is totally OT.

Specs:
I'm having an embedded Linux system running on a PPC405EP with 64 megs 
of RAM, some flash, but _no_ swap space. It runs a 2.4.20 kernel patched 
with drivers for my device.

Problem:
I have an application that is killed by the OOM (I guess) when it tries 
to "use" more memory than present on the system.
Bolied down, memory is allocated with "sbrk" and then touch'ed.

With "/proc/sys/vm/overcommit_memory" set to 2, I expected that "sbrk" 
would return "-1" (0xFFFFFFFF), but it doesn't, hence is 
terminated/killed by the kernel.

The same happens on another embedded Linux/2.4.17/i386, also without swap.

However, both my desktop Linux/2.4.18/i386 and Linux/2.6.5/i386 with 
swap does what I hoped:

# ./exhaust_mem
...
ffffffff

Out of memory
# #Yeaaaah!

Having searched the web, I see that this may be related with the fact 
that there is no swap enabled on either of my embedded devices.
Is this correct?
Can I do anything in order to get it the way I expected?

Best regards,
  Martin Egholm

=== exhaust_mem.c ===

#include <unistd.h>
#include <stdio.h>
#define SIZE 1000000

int main( int i )
{
   while ( 1 ) {
     char *v = sbrk( SIZE );
     char *p;

     printf( "%x\n\n", v );

     if ((long)v < 0) {
       fprintf(stderr, "Out of memory\n");
       exit(1);
     } // if

     for (p = v; p < v + SIZE; ++p) {
       *p = 42;
     } // for

   } // while
} // main


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