Re: Overcommit (OOM) problem on embedded device (PPChameleon)

[Martin Egholm Nielsen <martin@egholm-nielsen.dk>]

Hi Per,

> I think your main problem is that the stock 2.4.x kernel doesn't support
> ovecommit_memory type 2 (i believe)...
Doooh! You're so right!
I read the docs on overcommit_memory from 2.6 - stupid me!

> Look in mm/mmap.c and search for overcommit_memory, then do same
> in the sources for your redhat kernels.
I'll look into RH kernel to see if it isn't like you say :-)

> Perhaps there's a patch for it floating around somewhere? ;-)
Now, that would be really nice.
Though I have no idea of where to look!?

Thanks for clearing my mind!

BR,
  Martin

> 
> 
>>===== Original Message From Martin Egholm Nielsen <martin@egholm-nielsen.dk> 
> 
> =====
> 
>>Hi there,
>>
>>I hope this is the place to go...
>>
>>I have a some problems figuring out the OOM-killer and configuring the
>>overcommit_memory parameter. Hope someone here can guide me in the right
>>directions...
>>
>>Specs:
>>I'm having an embedded Linux system running on a PPC405EP (PPChameleon)
>>with 64 megs of RAM, some flash, but (ofcourse) 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 (see
>>test-application below).
>>
>>With "/proc/sys/vm/overcommit_memory" set to 2, I expected that "sbrk"
>>would return "-1L" (0xFFFFFFFF), but it doesn't, hence is
>>terminated/killed by the kernel.
>>
>>However, both my desktop Linux (RH 7.3)/2.4.18-10/i386 and Linux
>>(FC2)/2.6.5/i386 did what I expected:
>>
>># ./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 the embedded device.
>>However, I tried disabling the swap (commented in fstab), but the
>>desktop linux still behaves "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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> 
> 
> 
> 
>