lkml.org 
[lkml]   [2013]   [Nov]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/5] mm: compaction: reset cached scanner pfn's before reading them
On Mon, Nov 25, 2013 at 03:26:07PM +0100, Vlastimil Babka wrote:
> Compaction caches pfn's for its migrate and free scanners to avoid scanning
> the whole zone each time. In compact_zone(), the cached values are read to
> set up initial values for the scanners. There are several situations when
> these cached pfn's are reset to the first and last pfn of the zone,
> respectively. One of these situations is when a compaction has been deferred
> for a zone and is now being restarted during a direct compaction, which is also
> done in compact_zone().
>
> However, compact_zone() currently reads the cached pfn's *before* resetting
> them. This means the reset doesn't affect the compaction that performs it, and
> with good chance also subsequent compactions, as update_pageblock_skip() is
> likely to be called and update the cached pfn's to those being processed.
> Another chance for a successful reset is when a direct compaction detects that
> migration and free scanners meet (which has its own problems addressed by
> another patch) and sets update_pageblock_skip flag which kswapd uses to do the
> reset because it goes to sleep.
>
> This is clearly a bug that results in non-deterministic behavior, so this patch
> moves the cached pfn reset to be performed *before* the values are read.
>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Rik van Riel <riel@redhat.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Acked-by: Mel Gorman <mgorman@suse.de>

--
Mel Gorman
SUSE Labs


\
 
 \ /
  Last update: 2013-11-26 11:41    [W:0.219 / U:0.192 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site