On Fri, Feb 07, 2014 at 10:36:13AM +0100, Vlastimil Babka wrote: > On 02/07/2014 06:08 AM, Joonsoo Kim wrote: > > suitable_migration_target() checks that pageblock is suitable for > > migration target. In isolate_freepages_block(), it is called on every > > page and this is inefficient. So make it called once per pageblock. > > Hmm but in sync compaction, compact_checklock_irqsave() may drop the zone->lock, > reschedule and reacquire it and thus possibly invalidate your previous check. Async > compaction is ok as that will quit immediately. So you could probably communicate that > this happened and invalidate checked_pageblock in such case. Or maybe this would not > happen too enough to worry about rare suboptimal migrations? So, the result of previous check can be changed only if *this* pageblock's migratetype is changed while we drop the lock. I guess that this is really rare event, and, in this case, this pageblock already has mixed migratetype pages, so it has no serious problem. Thanks. -- 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>