From: Hugh Dickins <hughd@google.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mel Gorman <mgorman@suse.de>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Rik van Riel <riel@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Vlastimil Babka <vbabka@suse.cz>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH] mm, vmscan: do not loop on too_many_isolated for ever
Date: Wed, 19 Jul 2017 18:54:40 -0700 (PDT) [thread overview]
Message-ID: <alpine.LSU.2.11.1707191823190.2445@eggly.anvils> (raw)
In-Reply-To: <20170710074842.23175-1-mhocko@kernel.org>
On Mon, 10 Jul 2017, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>
> 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 <mgorman@suse.de>
> Tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> 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
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next prev parent reply other threads:[~2017-07-20 1:54 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-10 7:48 [PATCH] mm, vmscan: do not loop on too_many_isolated for ever Michal Hocko
2017-07-10 13:16 ` Vlastimil Babka
2017-07-10 13:58 ` Rik van Riel
2017-07-10 16:58 ` Johannes Weiner
2017-07-10 17:09 ` Michal Hocko
2017-07-19 22:20 ` Andrew Morton
2017-07-20 6:56 ` Michal Hocko
2017-07-21 23:01 ` Andrew Morton
2017-07-24 6:50 ` Michal Hocko
2017-07-20 1:54 ` Hugh Dickins [this message]
2017-07-20 10:44 ` Tetsuo Handa
2017-07-24 7:01 ` Hugh Dickins
2017-07-24 11:12 ` Tetsuo Handa
2017-07-20 13:22 ` Michal Hocko
2017-07-24 7:03 ` Hugh Dickins
-- strict thread matches above, loose matches on Subject: below --
2017-03-07 13:30 Michal Hocko
2017-03-07 19:52 ` Rik van Riel
2017-03-08 9:21 ` Michal Hocko
2017-03-08 15:54 ` Rik van Riel
2017-03-09 9:12 ` Michal Hocko
2017-03-09 14:16 ` Rik van Riel
2017-03-09 14:59 ` Michal Hocko
2017-03-09 18:05 ` Johannes Weiner
2017-03-09 22:18 ` Rik van Riel
2017-03-10 10:27 ` Michal Hocko
2017-03-10 10:20 ` Michal Hocko
2017-03-10 11:44 ` Tetsuo Handa
2017-03-21 10:37 ` Tetsuo Handa
2017-04-23 10:24 ` Tetsuo Handa
2017-04-24 12:39 ` Stanislaw Gruszka
2017-04-24 13:06 ` Tetsuo Handa
2017-04-25 6:33 ` Stanislaw Gruszka
2017-06-30 0:14 ` Tetsuo Handa
2017-06-30 13:32 ` Michal Hocko
2017-06-30 15:59 ` Tetsuo Handa
2017-06-30 16:19 ` Michal Hocko
2017-07-01 11:43 ` Tetsuo Handa
2017-07-05 8:19 ` Michal Hocko
2017-07-05 8:20 ` Michal Hocko
2017-07-06 10:48 ` Tetsuo Handa
2017-03-09 14:31 ` Mel Gorman
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