From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Weiner Subject: Re: [PATCH] mm: memcontrol: fix occasional OOMs due to proportional memory.low reclaim Date: Mon, 23 Aug 2021 13:48:43 -0400 Message-ID: References: <20210817180506.220056-1-hannes@cmpxchg.org> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=gbkRpn8OvHDvVhkug5/SCecw4iR6zEDgQeKV01fnIoo=; b=upkSxN2nnvY2Wv/MwUo3Qk+bN9RsxVHHPTcUHGhtMHImyRfryeKTsloFifEFrqdlt0 UxVtQai+tAQNcsIJ818me8Yhi3/bMHiaU7UglvqElSdxuOBTPg8BCOnN3T1AJfORwqcH NYTKsEACcfB06lkK8E4ps1ukwzCLeG8yfT85LndESHBE7pMmxUCgd78URSV2DpFKMKNs 5j1L94LSJYWhTz1Yyq8X6ZJU0F/PJxu6jlgN3V1E7rR727XeyxqXOvVGAY1aVcOmGrAW 7SpfwdKSRYCa67kYAD3SULGslNCC8EhJZcPuSsdvmwK1YPuq5Us1QyWndADVs8b5Lf83 KDZQ== Content-Disposition: inline In-Reply-To: List-ID: Content-Type: text/plain; charset="iso-8859-1" To: Michal =?iso-8859-1?Q?Koutn=FD?= Cc: Andrew Morton , Leon Yang , Chris Down , Roman Gushchin , Michal Hocko , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kernel-team-b10kYP2dOMg@public.gmane.org Hi Michal, On Mon, Aug 23, 2021 at 06:09:29PM +0200, Michal Koutn=FD wrote: > Hello >=20 > (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 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 =3D low; > > + sc->memcg_low_skipped =3D 1; >=20 > 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): >=20 > > The number of times the cgroup is reclaimed due to high memory > > pressure even though its usage is under the low boundary, >=20 > 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.