On Tue, Dec 9, 2014 at 5:59 PM, Mel Gorman <mgorman@xxxxxxx> wrote: > On Tue, Dec 09, 2014 at 03:40:35PM +0800, Weijie Yang wrote: >> If the free page and its buddy has different zone id, the current >> zone->lock cann't prevent buddy page getting allocated, this could >> trigger VM_BUG_ON_PAGE in a very tiny chance: >> > > Under what circumstances can a buddy page be allocated without the > zone->lock? Any parallel allocation from that zone that takes place will > be from the per-cpu allocator and should not be affected by this. Have > you actually hit this race? My description maybe not clear, if the free page and its buddy is not at the same zone, the holding zone->lock cann't prevent buddy page getting allocated. zone_1->lock prevents the freeing page getting allocated zone_2->lock prevents the buddy page getting allocated they are not the same zone->lock. I found it when review the code, not a running test. However, if we cann't remove the zone_id check statement, I think we should handle this rare race. If I miss something or make a mistake, please let me know. Thanks > -- > 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>