Re: OOM killer code in 2.6 kernel

John Richard Moser
2005-10-18T18:48:47Z

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

So basically you discovered:

- OOM activated due to say 512K free RAM (OOM happens before this IIRC
but eh)
- OOM kills process to give 127M free RAM
- Other CPU wants 4M RAM, so far 3M are free from killed process
- ANOTHER OOM kill happens to free up another 35M of RAM

Looks like a race condition?

Petrovic, Boban wrote:
> I have stumbled upon very interesting and in other hand very hard
> problem. I am trying to integrate code which introduces process
> protection from OOM killer action in cases when there is not enough RAM
> in the system. The code works fine on architectures like ppc32, ppc64
> and arm XScale. On Intel Xeon and Pentium M architectures with disabled
> SMP and HighMem support in the kernel the code also works fine. Problem
> begins if I turn on SMP and HighMem. I am using a test case which work
> following way: when child is forked both parent and child malloc amount
> of memory which when summed together exceed amount of memory available
> on system; parent is than protected. On the Intel architectures with SMP
> and HighMem on I experience that OOM kills many processes in addition to
> child process like sshd, portmap, bash, xinetd, etc. Number of killed
> processes vary from one test execution to other. As, I pointed out
> earlier, the code works fine only when SMP and HighMem are off. Any
> other combination of these options still causes the problem. I am using
> heavily patched Linux 2.6.10 kernel, with Kernel preempt turned off (the
> problem occurs with vanilla 2.6.14rc2 kernel also). The targets I have
> tested so far don't use swap device, and they have RAM in amounts
> starting from 1Gb.
> What I discovered so far is that when OOM sends SIGKILL to process,
> memory owned by process is not released as quickly as system would like.
> Processes running on other processors jump into OOM and eventually more
> processes get killed. I introduced changes to mm/page_alloc.c ->
> __alloc_pages() function which suppress more than one processor to enter
> the OOM code, and also I reduced number of OOM calls to one call per
> second for allowed processor. The idea is to give enough time to process
> marked to be killed to release pages. The change works fine for one of
> the targets but isn't working for other Intel boards.
> I need more insight on what might cause slow releasing of pages, when
> this release occurs and which part of kernel is in charge of that.
> Please CC me with your replies.
>
> Thanks,
> Boban
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>

- --
All content of all messages exchanged herein are left in the
Public Domain, unless otherwise explicitly stated.

Creative brains are a valuable, limited resource. They shouldn't be
wasted on re-inventing the wheel when there are so many fascinating
new problems waiting out there.
-- Eric Steven Raymond
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.1 (GNU/Linux)
Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org

iD8DBQFDVUL1hDd4aOud5P8RAoGvAJ9jSA5XF+WS625Ha0WJQEI49oey+QCdHj78
XL5rgwxIfmh9MyfJR8hrSlE=
=b8pR
-----END PGP SIGNATURE-----