2016-05-04 17:56 GMT+09:00 Michal Hocko <mhocko@xxxxxxxxxx>: > On Wed 04-05-16 15:31:12, Joonsoo Kim wrote: >> On Wed, May 04, 2016 at 03:01:24PM +0900, Joonsoo Kim wrote: >> > On Wed, Apr 20, 2016 at 03:47:25PM -0400, Michal Hocko wrote: > [...] >> > > @@ -3408,6 +3456,17 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, >> > > no_progress_loops)) >> > > goto retry; >> > > >> > > + /* >> > > + * It doesn't make any sense to retry for the compaction if the order-0 >> > > + * reclaim is not able to make any progress because the current >> > > + * implementation of the compaction depends on the sufficient amount >> > > + * of free memory (see __compaction_suitable) >> > > + */ >> > > + if (did_some_progress > 0 && >> > > + should_compact_retry(order, compact_result, >> > > + &migration_mode, compaction_retries)) >> > >> > Checking did_some_progress on each round have subtle corner case. Think >> > about following situation. >> > >> > round, compaction, did_some_progress, compaction >> > 0, defer, 1 >> > 0, defer, 1 >> > 0, defer, 1 >> > 0, defer, 1 >> > 0, defer, 0 >> >> Oops...Example should be below one. >> >> 0, defer, 1 >> 1, defer, 1 >> 2, defer, 1 >> 3, defer, 1 >> 4, defer, 0 > > I am not sure I understand. The point of the check is that if the > reclaim doesn't make _any_ progress then checking the result of the > compaction after it didn't lead to a successful allocation just doesn't > make any sense. Even if this round (#4) doesn't reclaim any pages, previous rounds (#0, #1, #2, #3) would reclaim enough pages to succeed future compaction attempt. 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>