On 11/25/2013 09:26 AM, 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 <mgor...@suse.de> > Cc: Rik van Riel <r...@redhat.com> > Signed-off-by: Vlastimil Babka <vba...@suse.cz>
Acked-by: Rik van Riel <r...@redhat.com> -- All rights reversed -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
