On Tue, 1 Jun 2010 12:29:41 +0900 (JST) KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> wrote: > > With this patch applied, it is possible that when do_try_to_free_pages() > > calls shrink_zones() for priority 0 that shrink_zones() may return 1 > > indicating progress, even though no pages may have been reclaimed. > > Because this is a cgroup operation, scanning_global_lru() is false and > > the following portion of do_try_to_free_pages() fails to set ret=0. > > > if (ret && scanning_global_lru(sc)) > > > ret = sc->nr_reclaimed; > > This leaves ret=1 indicating that do_try_to_free_pages() reclaimed 1 > > page even though it did not reclaim any pages. Therefore > > mem_cgroup_force_empty() erroneously believes that > > try_to_free_mem_cgroup_pages() is making progress (one page at a time), > > so there is an endless loop. > > Good catch! > > Yeah, your analysis is fine. thank you for both your testing and > making analysis. > > Unfortunatelly, this logic need more fix. because It have already been > corrupted by another regression. my point is, if priority==0 reclaim > failure occur, "ret = sc->nr_reclaimed" makes no sense at all. > > The fixing patch is here. What do you think? > > > > From 49a395b21fe1b2f864112e71d027ffcafbdc9fc0 Mon Sep 17 00:00:00 2001 > From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Date: Tue, 1 Jun 2010 11:29:50 +0900 > Subject: [PATCH] vmscan: Fix do_try_to_free_pages() return value when priority==0 reclaim failure > > Greg Thelen reported recent Johannes's stack diet patch makes kernel > hang. His test is following. > > mount -t cgroup none /cgroups -o memory > mkdir /cgroups/cg1 > echo $$ > /cgroups/cg1/tasks > dd bs=1024 count=1024 if=/dev/null of=/data/foo > echo $$ > /cgroups/tasks > echo 1 > /cgroups/cg1/memory.force_empty > > Actually, This OOM hard to try logic have been corrupted > since following two years old patch. > > commit a41f24ea9fd6169b147c53c2392e2887cc1d9247 > Author: Nishanth Aravamudan <nacc@xxxxxxxxxx> > Date: Tue Apr 29 00:58:25 2008 -0700 > > page allocator: smarter retry of costly-order allocations > > Original intention was "return success if the system have shrinkable > zones though priority==0 reclaim was failure". But the above patch > changed to "return nr_reclaimed if .....". Oh, That forgot nr_reclaimed > may be 0 if priority==0 reclaim failure. > > And Johannes's patch made more corrupt. Originally, priority==0 recliam > failure on memcg return 0, but this patch changed to return 1. It > totally confused memcg. > > This patch fixes it completely. > > Reported-by: Greg Thelen <gthelen@xxxxxxxxxx> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Thank you very much!! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>