On Tue, Apr 15, 2014 at 11:18:26AM +0200, Vlastimil Babka wrote: > The compaction freepage scanner implementation in isolate_freepages() starts > by taking the current cc->free_pfn value as the first pfn. In a for loop, it > scans from this first pfn to the end of the pageblock, and then subtracts > pageblock_nr_pages from the first pfn to obtain the first pfn for the next > for loop iteration. > > This means that when cc->free_pfn starts at offset X rather than being aligned > on pageblock boundary, the scanner will start at offset X in all scanned > pageblock, ignoring potentially many free pages. Currently this can happen when > a) zone's end pfn is not pageblock aligned, or > b) through zone->compact_cached_free_pfn with CONFIG_HOLES_IN_ZONE enabled and > a hole spanning the beginning of a pageblock > > This patch fixes the problem by aligning the initial pfn in isolate_freepages() > to pageblock boundary. This also allows to replace the end-of-pageblock > alignment within the for loop with a simple pageblock_nr_pages increment. > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> > Reported-by: Heesub Shin <heesub.shin@xxxxxxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxx> > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> > Cc: Michal Nazarewicz <mina86@xxxxxxxxxx> > Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > Cc: Christoph Lameter <cl@xxxxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxx> > --- > mm/compaction.c | 22 ++++++++++++---------- > 1 file changed, 12 insertions(+), 10 deletions(-) Acked-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> -- 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>