On Sun, 11 Aug 2013 18:46:08 -0700 Lisa Du <cldu@xxxxxxxxxxx> wrote: > This patch is based on KOSAKI's work and I add a little more > description, please refer https://lkml.org/lkml/2012/6/14/74. > > Currently, I found system can enter a state that there are lots > of free pages in a zone but only order-0 and order-1 pages which > means the zone is heavily fragmented, then high order allocation > could make direct reclaim path's long stall(ex, 60 seconds) > especially in no swap and no compaciton enviroment. This problem > happened on v3.4, but it seems issue still lives in current tree, > the reason is do_try_to_free_pages enter live lock: > > kswapd will go to sleep if the zones have been fully scanned > and are still not balanced. As kswapd thinks there's little point > trying all over again to avoid infinite loop. Instead it changes > order from high-order to 0-order because kswapd think order-0 is the > most important. Look at 73ce02e9 in detail. If watermarks are ok, > kswapd will go back to sleep and may leave zone->all_unreclaimable = 0. > It assume high-order users can still perform direct reclaim if they wish. > > Direct reclaim continue to reclaim for a high order which is not a > COSTLY_ORDER without oom-killer until kswapd turn on zone->all_unreclaimble. > This is because to avoid too early oom-kill. So it means direct_reclaim > depends on kswapd to break this loop. > > In worst case, direct-reclaim may continue to page reclaim forever > when kswapd sleeps forever until someone like watchdog detect and finally > kill the process. As described in: > http://thread.gmane.org/gmane.linux.kernel.mm/103737 > > We can't turn on zone->all_unreclaimable from direct reclaim path > because direct reclaim path don't take any lock and this way is racy. > Thus this patch removes zone->all_unreclaimable field completely and > recalculates zone reclaimable state every time. > > Note: we can't take the idea that direct-reclaim see zone->pages_scanned > directly and kswapd continue to use zone->all_unreclaimable. Because, it > is racy. commit 929bea7c71 (vmscan: all_unreclaimable() use > zone->all_unreclaimable as a name) describes the detail. I did this to fix the build: --- a/mm/migrate.c~mm-vmscan-fix-do_try_to_free_pages-livelock-fix-2 +++ a/mm/migrate.c @@ -1471,7 +1471,7 @@ static bool migrate_balanced_pgdat(struc if (!populated_zone(zone)) continue; - if (zone->all_unreclaimable) + if (!zone_reclaimable(zone)) continue; /* Avoid waking kswapd by allocating pages_to_migrate pages. */ Please review and runtime test it? -- 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>