lkml.org 
[lkml]   [2012]   [Jul]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [ 13/40] vmscan: shrinker->nr updates race and go wrong
From
Date
On Thu, 2012-07-26 at 14:29 -0700, Greg Kroah-Hartman wrote:
> From: Greg KH <gregkh@linuxfoundation.org>
>
> 3.0-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Dave Chinner <dchinner@redhat.com>
>
> commit acf92b485cccf028177f46918e045c0c4e80ee10 upstream.
>
> Stable note: Not tracked in Bugzilla. This patch reduces excessive
> reclaim of slab objects reducing the amount of information
> that has to be brought back in from disk.
>
> shrink_slab() allows shrinkers to be called in parallel so the
> struct shrinker can be updated concurrently. It does not provide any
> exclusio for such updates, so we can get the shrinker->nr value
> increasing or decreasing incorrectly.
>
> As a result, when a shrinker repeatedly returns a value of -1 (e.g.
> a VFS shrinker called w/ GFP_NOFS), the shrinker->nr goes haywire,
> sometimes updating with the scan count that wasn't used, sometimes
> losing it altogether. Worse is when a shrinker does work and that
> update is lost due to racy updates, which means the shrinker will do
> the work again!
>
> Fix this by making the total_scan calculations independent of
> shrinker->nr, and making the shrinker->nr updates atomic w.r.t. to
> other updates via cmpxchg loops.
[...]
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -251,17 +251,29 @@ unsigned long shrink_slab(struct shrink_
> unsigned long total_scan;
[...]
> + total_scan += delta;
> + if (total_scan < 0) {
[...]

This condition is never true since total_scan is unsigned.
I think 3.0.y needs this as well:

commit 635697c663f38106063d5659f0cf2e45afcd4bb5
Author: Konstantin Khlebnikov <khlebnikov@openvz.org>
Date: Thu Dec 8 14:33:51 2011 -0800

vmscan: fix initial shrinker size handling

Ben.

--
Ben Hutchings
Man invented language to satisfy his deep need to complain. - Lily Tomlin
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2012-07-29 22:41    [W:0.928 / U:0.724 seconds]
©2003-2014 Jasper Spaans. Advertise on this site