Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933741AbdGTByt (ORCPT ); Wed, 19 Jul 2017 21:54:49 -0400 Received: from mail-pf0-f181.google.com ([209.85.192.181]:32965 "EHLO mail-pf0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933360AbdGTBys (ORCPT ); Wed, 19 Jul 2017 21:54:48 -0400 Date: Wed, 19 Jul 2017 18:54:40 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Michal Hocko cc: Andrew Morton , Mel Gorman , Tetsuo Handa , Rik van Riel , Johannes Weiner , Vlastimil Babka , linux-mm@kvack.org, LKML , Michal Hocko Subject: Re: [PATCH] mm, vmscan: do not loop on too_many_isolated for ever In-Reply-To: <20170710074842.23175-1-mhocko@kernel.org> Message-ID: References: <20170710074842.23175-1-mhocko@kernel.org> User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5362 Lines: 118 On Mon, 10 Jul 2017, Michal Hocko wrote: > From: Michal Hocko > > Tetsuo Handa has reported [1][2][3]that direct reclaimers might get stuck > in too_many_isolated loop basically for ever because the last few pages > on the LRU lists are isolated by the kswapd which is stuck on fs locks > when doing the pageout or slab reclaim. This in turn means that there is > nobody to actually trigger the oom killer and the system is basically > unusable. > > too_many_isolated has been introduced by 35cd78156c49 ("vmscan: throttle > direct reclaim when too many pages are isolated already") to prevent > from pre-mature oom killer invocations because back then no reclaim > progress could indeed trigger the OOM killer too early. But since the > oom detection rework 0a0337e0d1d1 ("mm, oom: rework oom detection") > the allocation/reclaim retry loop considers all the reclaimable pages > and throttles the allocation at that layer so we can loosen the direct > reclaim throttling. > > Make shrink_inactive_list loop over too_many_isolated bounded and returns > immediately when the situation hasn't resolved after the first sleep. > Replace congestion_wait by a simple schedule_timeout_interruptible because > we are not really waiting on the IO congestion in this path. > > Please note that this patch can theoretically cause the OOM killer to > trigger earlier while there are many pages isolated for the reclaim > which makes progress only very slowly. This would be obvious from the oom > report as the number of isolated pages are printed there. If we ever hit > this should_reclaim_retry should consider those numbers in the evaluation > in one way or another. > > [1] http://lkml.kernel.org/r/201602092349.ACG81273.OSVtMJQHLOFOFF@I-love.SAKURA.ne.jp > [2] http://lkml.kernel.org/r/201702212335.DJB30777.JOFMHSFtVLQOOF@I-love.SAKURA.ne.jp > [3] http://lkml.kernel.org/r/201706300914.CEH95859.FMQOLVFHJFtOOS@I-love.SAKURA.ne.jp > > Acked-by: Mel Gorman > Tested-by: Tetsuo Handa > Signed-off-by: Michal Hocko > --- > Hi, > I am resubmitting this patch previously sent here > http://lkml.kernel.org/r/20170307133057.26182-1-mhocko@kernel.org. > > Johannes and Rik had some concerns that this could lead to premature > OOM kills. I agree with them that we need a better throttling > mechanism. Until now we didn't give the issue described above a high > priority because it usually required a really insane workload to > trigger. But it seems that the issue can be reproduced also without > having an insane number of competing threads [3]. > > Moreover, the issue also triggers very often while testing heavy memory > pressure and so prevents further development of hardening of that area > (http://lkml.kernel.org/r/201707061948.ICJ18763.tVFOQFOHMJFSLO@I-love.SAKURA.ne.jp). > Tetsuo hasn't seen any negative effect of this patch in his oom stress > tests so I think we should go with this simple patch for now and think > about something more robust long term. > > That being said I suggest merging this (after spending the full release > cycle in linux-next) for the time being until we come up with a more > clever solution. > > mm/vmscan.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index c15b2e4c47ca..4ae069060ae5 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1713,9 +1713,15 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, > int file = is_file_lru(lru); > struct pglist_data *pgdat = lruvec_pgdat(lruvec); > struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; > + bool stalled = false; > > while (unlikely(too_many_isolated(pgdat, file, sc))) { > - congestion_wait(BLK_RW_ASYNC, HZ/10); > + if (stalled) > + return 0; > + > + /* wait a bit for the reclaimer. */ > + schedule_timeout_interruptible(HZ/10); > + stalled = true; > > /* We are about to die and free our memory. Return now. */ > if (fatal_signal_pending(current)) > -- You probably won't welcome getting into alternatives at this late stage; but after hacking around it one way or another because of its pointless lockups, I lost patience with that too_many_isolated() loop a few months back (on realizing the enormous number of pages that may be isolated via migrate_pages(2)), and we've been running nicely since with something like: bool got_mutex = false; if (unlikely(too_many_isolated(pgdat, file, sc))) { if (mutex_lock_killable(&pgdat->too_many_isolated)) return SWAP_CLUSTER_MAX; got_mutex = true; } ... if (got_mutex) mutex_unlock(&pgdat->too_many_isolated); Using a mutex to provide the intended throttling, without an infinite loop or an arbitrary delay; and without having to worry (as we often did) about whether those numbers in too_many_isolated() are really appropriate. No premature OOMs complained of yet. But that was on a different kernel, and there I did have to make sure that PF_MEMALLOC always prevented us from nesting: I'm not certain of that in the current kernel (but do remember Johannes changing the memcg end to make it use PF_MEMALLOC too). I offer the preview above, to see if you're interested in that alternative: if you are, then I'll go ahead and make it into an actual patch against v4.13-rc. Hugh