From: Johannes Weiner <hannes@cmpxchg.org>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Leon Yang <lnyng@fb.com>, Chris Down <chris@chrisdown.name>,
Roman Gushchin <guro@fb.com>, Michal Hocko <mhocko@suse.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH] mm: memcontrol: fix occasional OOMs due to proportional memory.low reclaim
Date: Mon, 23 Aug 2021 13:48:43 -0400 [thread overview]
Message-ID: <YSPfe4yf2fRdzijh@cmpxchg.org> (raw)
In-Reply-To: <YSPIOZOVG2qplLIW@blackbook>
Hi Michal,
On Mon, Aug 23, 2021 at 06:09:29PM +0200, Michal Koutný wrote:
> Hello
>
> (and sorry for a belated reply).
It's never too late, thanks for taking a look.
> On Tue, Aug 17, 2021 at 02:05:06PM -0400, Johannes Weiner <hannes@cmpxchg.org> wrote:
> > @@ -2576,6 +2578,15 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
> > [...]
> > + /* memory.low scaling, make sure we retry before OOM */
> > + if (!sc->memcg_low_reclaim && low > min) {
> > + protection = low;
> > + sc->memcg_low_skipped = 1;
>
> IIUC, this won't result in memory.events:low increment although the
> effect is similar (breaching (partial) memory.low protection) and signal
> to the user is comparable (overcommited memory.low).
Good observation. I think you're right, we should probably count such
partial breaches as LOW events as well.
Note that this isn't new behavior. My patch merely moved this part
from mem_cgroup_protection():
- if (in_low_reclaim)
- return READ_ONCE(memcg->memory.emin);
Even before, if we retried due to just one (possibly insignificant)
cgroup below low, we'd ignore proportional reclaim and partially
breach ALL protected cgroups, while only counting a low event for the
one group that is usage < low.
> Admittedly, this patch's behavior adheres to the current documentation
> (Documentation/admin-guide/cgroup-v2.rst):
>
> > The number of times the cgroup is reclaimed due to high memory
> > pressure even though its usage is under the low boundary,
>
> however, that definition might not be what the useful indicator would
> be now.
> Is it worth including these partial breaches into memory.events:low?
I think it is. How about:
"The number of times the cgroup's memory.low-protected memory was
reclaimed in order to avoid OOM during high memory pressure."
And adding a MEMCG_LOW event to partial breaches. BTW, the comment
block above this code is also out-of-date, because it says we're
honoring memory.low on the retries, but that's not the case.
I'll prepare a follow-up patch for these 3 things as well as the more
verbose comment that Michal Hocko asked for on the retry logic.
next prev parent reply other threads:[~2021-08-23 17:47 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-17 18:05 [PATCH] mm: memcontrol: fix occasional OOMs due to proportional memory.low reclaim Johannes Weiner
2021-08-17 18:44 ` Rik van Riel
2021-08-17 19:10 ` Shakeel Butt
2021-08-18 14:16 ` Johannes Weiner
2021-08-17 19:14 ` Andrew Morton
2021-08-17 19:45 ` Roman Gushchin
2021-08-18 14:15 ` Johannes Weiner
2021-08-18 20:18 ` Chris Down
2021-08-19 15:01 ` Michal Hocko
2021-08-19 20:38 ` Johannes Weiner
2021-08-20 15:44 ` Michal Hocko
2021-08-23 16:09 ` Michal Koutný
2021-08-23 17:48 ` Johannes Weiner [this message]
2021-08-24 13:01 ` Michal Koutný
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