Re: [Bug #14141] order 2 page allocation failures in iwlagn

Frans Pop
2009-10-02T09:11:52Z

On Thursday 01 October 2009, Rafael J. Wysocki wrote:
> The following bug entry is on the current list of known regressions
> introduced between 2.6.30 and 2.6.31. Please verify if it still should
> be listed and let me know (either way).
>
> Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=14141
> Subject : order 2 page allocation failures in iwlagn
> Submitter : Frans Pop <elendil-EIBgga6/0yRmR6Xm/wNWPw@public.gmane.org>
> Date : 2009-09-06 7:40 (26 days old)
> References : http://marc.info/?l=linux-kernel&m=125222287419691&w=4
> Handled-By : Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>

I'm not sure about this.

The error messages from failed allocations should now be a lot less as a
result of this commit:
commit f82a924cc88a5541df1d4b9d38a0968cd077a051
Author: Reinette Chatre <reinette.chatre-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Date: Thu Sep 17 10:43:56 2009 -0700
iwlwifi: reduce noise when skb allocation fails

That commit is in mainline, and I'm not sure if it is important enough for
a stable update (AFAICT it's not listed for 2.6.31.2).

That commit is mostly cosmetic, but possibly the real regression is not in
iwlagn but in the way memory is freed/defragmented. That aspect was also
reported by Bartlomiej (#14016) and was extensively discussed (without a
clear conclusion) here: http://lkml.org/lkml/2009/8/26/140.

My own feeling is that Bartlomiej is correct and that something has changed
since .29 and that on average we do have less higher order areas available
after the system has been in use for some time, but I can't substantiate
that. I do know that before .30 I had never seen the SKB allocation
errors.

Main problem is that it's hard to deliberately and reproducibly get the
system in a state where the errors occur.

I certainly do feel that the kernel should try to make sure higher order
allocations remain possible during system use. They are not only needed
shortly after boot: drivers can be loaded/unloaded at any time. OTOH Mel
probably does have a point that really high order GFP_ATOMIC allocations
by drivers make no sense [1].

Anyway, I have no problems with this BR being closed.

Cheers,
FJP

[1] <20090921133704.GO12726-wPRd99KPJ+uzQB+pC5nmwQ@public.gmane.org>