Hello Xishi, On Thu, Sep 06, 2012 at 10:35:39AM +0800, qiuxishi wrote: > On 2012/9/5 17:40, Mel Gorman wrote: > > > On Wed, Sep 05, 2012 at 04:26:02PM +0900, Minchan Kim wrote: > >> Like below, memory-hotplug makes race between page-isolation > >> and page-allocation so it can hit BUG_ON in __offline_isolated_pages. > >> > >> CPU A CPU B > >> > >> start_isolate_page_range > >> set_migratetype_isolate > >> spin_lock_irqsave(zone->lock) > >> > >> free_hot_cold_page(Page A) > >> /* without zone->lock */ > >> migratetype = get_pageblock_migratetype(Page A); > >> /* > >> * Page could be moved into MIGRATE_MOVABLE > >> * of per_cpu_pages > >> */ > >> list_add_tail(&page->lru, &pcp->lists[migratetype]); > >> > >> set_pageblock_isolate > >> move_freepages_block > >> drain_all_pages > > I think here is the problem you want to fix, it is not sure that pcp will be moved > into MIGRATE_ISOLATE list. They may be moved into MIGRATE_MOVABLE list because > page_private() maybe 2, it uses page_private() not get_pageblock_migratetype() > > So when finish migrating pages, the free pages from pcp may be allocated again, and > failed in check_pages_isolated(). > > drain_all_pages() > drain_local_pages() > drain_pages() > free_pcppages_bulk() > __free_one_page(page, zone, 0, page_private(page)) > > I reported this problem too. http://marc.info/?l=linux-mm&m=134555113706068&w=2 > How about this change: > free_pcppages_bulk() > __free_one_page(page, zone, 0, get_pageblock_migratetype(page)) I already explained why it was not good solution. Again, here it goes from my previous reply. " Anyway, I don't like your approach which I already considered because it hurts hotpath while the race is really unlikely. Get_pageblock_migratetype is never trivial. We should avoid the overhead in hotpath and move into memory-hotplug itself. Do you see my patch in https://patchwork.kernel.org/patch/1225081/ ? " -- 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>