Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755574AbdGSWUR (ORCPT ); Wed, 19 Jul 2017 18:20:17 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36352 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753695AbdGSWUP (ORCPT ); Wed, 19 Jul 2017 18:20:15 -0400 Date: Wed, 19 Jul 2017 15:20:14 -0700 From: Andrew Morton To: Michal Hocko Cc: Mel Gorman , Tetsuo Handa , Rik van Riel , Johannes Weiner , Vlastimil Babka , , LKML , Michal Hocko Subject: Re: [PATCH] mm, vmscan: do not loop on too_many_isolated for ever Message-Id: <20170719152014.53a861c57bcb636d6cd9d002@linux-foundation.org> In-Reply-To: <20170710074842.23175-1-mhocko@kernel.org> References: <20170710074842.23175-1-mhocko@kernel.org> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2931 Lines: 69 On Mon, 10 Jul 2017 09:48:42 +0200 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. Need to figure out which kernels to patch. Maybe just 4.13-rc after a week or two? > --- 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); a) if this task has signal_pending(), this falls straight through and I suspect the code breaks? b) replacing congestion_wait() with schedule_timeout_interruptible() means this task no longer contributes to load average here and it's a (slightly) user-visible change. c) msleep_interruptible() is nicer d) IOW, methinks we should be using msleep() here? > + stalled = true; > > /* We are about to die and free our memory. Return now. */ > if (fatal_signal_pending(current)) (Gets distracted by the thought that we should do s/msleep/msleep_uninterruptible/g)