On Wed, Jul 16, 2014 at 03:48:18PM +0200, Vlastimil Babka wrote: > Unlike the migration scanner, the free scanner remembers the beginning of the > last scanned pageblock in cc->free_pfn. It might be therefore rescanning pages > uselessly when called several times during single compaction. This might have > been useful when pages were returned to the buddy allocator after a failed > migration, but this is no longer the case. > > This patch changes the meaning of cc->free_pfn so that if it points to a > middle of a pageblock, that pageblock is scanned only from cc->free_pfn to the > end. isolate_freepages_block() will record the pfn of the last page it looked > at, which is then used to update cc->free_pfn. > > In the mmtests stress-highalloc benchmark, this has resulted in lowering the > ratio between pages scanned by both scanners, from 2.5 free pages per migrate > page, to 2.25 free pages per migrate page, without affecting success rates. > > With __GFP_NO_KSWAPD allocations, this appears to result in a worse ratio (2.1 > instead of 1.8), but page migration successes increased by 10%, so this could > mean that more useful work can be done until need_resched() aborts this kind > of compaction. > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > Reviewed-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx> > Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> > Acked-by: Minchan Kim <minchan@xxxxxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxx> -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>