On Thu, Apr 03, 2014 at 05:40:17PM +0200, Vlastimil Babka wrote: > For the MIGRATE_RESERVE pages, it is important they do not get misplaced > on free_list of other migratetype, otherwise the whole MIGRATE_RESERVE > pageblock might be changed to other migratetype in try_to_steal_freepages(). > > Currently, it is however possible for this to happen when MIGRATE_RESERVE > page is allocated on pcplist through rmqueue_bulk() as a fallback for other > desired migratetype, and then later freed back through free_pcppages_bulk() > without being actually used. This happens because free_pcppages_bulk() uses > get_freepage_migratetype() to choose the free_list, and rmqueue_bulk() calls > set_freepage_migratetype() with the *desired* migratetype and not the page's > original MIGRATE_RESERVE migratetype. > > This patch fixes the problem by moving the call to set_freepage_migratetype() > from rmqueue_bulk() down to __rmqueue_smallest() and __rmqueue_fallback() where > the actual page's migratetype (e.g. from which free_list the page is taken > from) is used. Note that this migratetype might be different from the > pageblock's migratetype due to freepage stealing decisions. This is OK, as page > stealing never uses MIGRATE_RESERVE as a fallback, and also takes care to leave > all MIGRATE_CMA pages on the correct freelist. > > Therefore, as an additional benefit, the call to get_pageblock_migratetype() > from rmqueue_bulk() when CMA is enabled, can be removed completely. This relies > on the fact that MIGRATE_CMA pageblocks are created only during system init, > and the above. The related is_migrate_isolate() check is also unnecessary, as > memory isolation has other ways to move pages between freelists, and drain > pcp lists containing pages that should be isolated. > The buffered_rmqueue() can also benefit from calling get_freepage_migratetype() > instead of get_pageblock_migratetype(). Nice description. > > A separate patch will add VM_BUG_ON checks for the invariant that for > MIGRATE_RESERVE and MIGRATE_CMA pageblocks, freepage_migratetype must equal to > pageblock_migratetype so that these pages always go to the correct free_list. > > Reported-by: Yong-Taek Lee <ytk.lee@xxxxxxxxxxx> > Reported-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> > Suggested-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > Suggested-by: Mel Gorman <mgorman@xxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxx> > Cc: Michal Nazarewicz <mina86@xxxxxxxxxx> > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: Minchan Kim <minchan@xxxxxxxxxx> -- Kind regards, Minchan Kim -- 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>