On Mon, Aug 05, 2013 at 12:53:43AM -0400, Johannes Weiner wrote: > On Sun, Aug 04, 2013 at 07:26:38PM -0700, Lisa Du wrote: > > From: Lisa Du <cldu@xxxxxxxxxxx> > > Date: Mon, 5 Aug 2013 09:26:57 +0800 > > Subject: [PATCH] mm: vmscan: fix do_try_to_free_pages() livelock > > > > 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. > > > > Change-Id: If3b44e33e400c1db0e42a5e2fc9ebc7a265f2aae > > Cc: Aaditya Kumar <aaditya.kumar.30@xxxxxxxxx> > > Cc: Ying Han <yinghan@xxxxxxxxxx> > > Cc: Nick Piggin <npiggin@xxxxxxxxx> > > Acked-by: Rik van Riel <riel@xxxxxxxxxx> > > Cc: Michal Hocko <mhocko@xxxxxxx> > > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > > Cc: Mel Gorman <mel@xxxxxxxxx> > > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> > > Cc: Minchan Kim <minchan.kim@xxxxxxxxx> > > Cc: Bob Liu <lliubbo@xxxxxxxxx> > > Cc: Neil Zhang <zhangwm@xxxxxxxxxxx> > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > > Signed-off-by: Lisa Du <cldu@xxxxxxxxxxx> > > Wow, the original patch is over a year old. As before: > > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> > > One comment: > > > @@ -2244,8 +2244,8 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc) > > if (global_reclaim(sc)) { > > if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) > > continue; > > - if (zone->all_unreclaimable && > > - sc->priority != DEF_PRIORITY) > > + if (!zone_reclaimable(zone) && > > + sc->priority != DEF_PRIORITY) > > continue; /* Let kswapd poll it */ > > if (IS_ENABLED(CONFIG_COMPACTION)) { > > /* > > As Michal pointed out last time, it would make sense to reorder these > checks because the priority test is much lighter than calculating the > reclaimable pages. Would make DEF_PRIORITY cycles slightly lighter. > > It's not necessarily about the performance but if we leave it like > this there will be boring patches in the future that change it to do > the light-weight check first, claiming it will improve performance, > and then somebody else will ask them for benchmark results and they > will ask how page reclaim is usually benchmarked and everybody will > shrug their shoulders and go "good question" until somebody blames > memory cgroups. > > So, please, save us from all this drama and reorder the checks. +1 I don't want to pay my money for soap opera. -- 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>