From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f197.google.com (mail-pl1-f197.google.com [209.85.214.197]) by kanga.kvack.org (Postfix) with ESMTP id 0AF6C8E0002 for ; Wed, 16 Jan 2019 21:41:39 -0500 (EST) Received: by mail-pl1-f197.google.com with SMTP id g13so5149845plo.10 for ; Wed, 16 Jan 2019 18:41:38 -0800 (PST) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id k11sor289032pll.39.2019.01.16.18.41.37 for (Google Transport Security); Wed, 16 Jan 2019 18:41:37 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 12.2 \(3445.102.3\)) Subject: Re: memory cgroup pagecache and inode problem From: Fam Zheng In-Reply-To: Date: Thu, 17 Jan 2019 10:41:31 +0800 Content-Transfer-Encoding: quoted-printable Message-Id: <99AFB530-E90E-4784-B199-FA3F91171649@bytedance.com> References: <15614FDC-198E-449B-BFAF-B00D6EF61155@bytedance.com> <97A4C2CA-97BA-46DB-964A-E44410BB1730@bytedance.com> <9B56B884-8FDD-4BB5-A6CA-AD7F84397039@bytedance.com> Sender: owner-linux-mm@kvack.org List-ID: To: Yang Shi Cc: Fam Zheng , cgroups@vger.kernel.org, Linux MM , tj@kernel.org, Johannes Weiner , lizefan@huawei.com, Michal Hocko , Vladimir Davydov , duanxiongchun@bytedance.com, =?utf-8?B?5byg5rC46IKD?= , liuxiaozhou@bytedance.com > On Jan 17, 2019, at 05:06, Yang Shi wrote: >=20 > On Tue, Jan 15, 2019 at 7:52 PM Fam Zheng = wrote: >>=20 >>=20 >>=20 >>> On Jan 16, 2019, at 08:50, Yang Shi wrote: >>>=20 >>> On Thu, Jan 10, 2019 at 12:30 AM Fam Zheng = wrote: >>>>=20 >>>>=20 >>>>=20 >>>>> On Jan 10, 2019, at 13:36, Yang Shi wrote: >>>>>=20 >>>>> On Sun, Jan 6, 2019 at 9:10 PM Fam Zheng = wrote: >>>>>>=20 >>>>>>=20 >>>>>>=20 >>>>>>> On Jan 5, 2019, at 03:36, Yang Shi wrote: >>>>>>>=20 >>>>>>>=20 >>>>>>> drop_caches would drop all page caches globally. You may not = want to >>>>>>> drop the page caches used by other memcgs. >>>>>>=20 >>>>>> We=E2=80=99ve tried your async force_empty patch (with a = modification to default it to true to make it transparently enabled for = the sake of testing), and for the past few days the stale mem cgroups = still accumulate, up to 40k. >>>>>>=20 >>>>>> We=E2=80=99ve double checked that the force_empty routines are = invoked when a mem cgroup is offlined. But this doesn=E2=80=99t look = very effective so far. Because, once we do `echo 1 > = /proc/sys/vm/drop_caches`, all the groups immediately go away. >>>>>>=20 >>>>>> This is a bit unexpected. >>>>>>=20 >>>>>> Yang, could you hint what are missing in the force_empty = operation, compared to a blanket drop cache? >>>>>=20 >>>>> Drop caches does invalidate pages inode by inode. But, memcg >>>>> force_empty does call memcg direct reclaim. >>>>=20 >>>> But force_empty touches things that drop_caches doesn=E2=80=99t? If = so then maybe combining both approaches is more reliable. Since like you = said, >>>=20 >>> AFAICS, force_empty may unmap pages, but drop_caches doesn't. >>>=20 >>>> dropping _all_ pages is usually too much thus not desired, we may = want to somehow limit the dropped caches to those that are in the memory = cgroup in question. What do you think? >>>=20 >>> This is what force_empty is supposed to do. But, as your test shows >>> some page cache may still remain after force_empty, then cause = offline >>> memcgs accumulated. I haven't figured out what happened. You may = try >>> what Michal suggested. >>=20 >> None of the existing patches helped so far, but we suspect that the = pages cannot be locked at the force_empty moment. We have being working = on a =E2=80=9Cretry=E2=80=9D patch which does solve the problem. We=E2=80=99= ll do more tracing (to have a better understanding of the issue) and = post the findings and/or the patch later. Thanks. >=20 > You mean it solves the problem by retrying more times? Actually, I'm > not sure if you have swap setup in your test, but force_empty does do > swap if swap is on. This may cause it can't reclaim all the page cache > in 5 retries. I have a patch within that series to skip swap. Basically yes, retrying solves the problem. But compared to immediate = retries, a scheduled retry in a few seconds is much more effective. We don=E2=80=99t have swap on. What do you mean by 5 retries? I=E2=80=99m still a bit lost in the LRU = code and patches. >=20 > Yang >=20 >>=20 >> Fam >>=20 >>>=20 >>> Yang >>>=20 >>>>=20 >>>>=20 >>>>>=20 >>>>> Offlined memcgs will not go away if there is still page charged. = Maybe >>>>> relate to per cpu memcg stock. I recall there are some commits = which >>>>> do solve the per cpu page counter cache problem. >>>>>=20 >>>>> 591edfb10a94 mm: drain memcg stocks on css offlining >>>>> d12c60f64cf8 mm: memcontrol: drain memcg stock on force_empty >>>>> bb4a7ea2b144 mm: memcontrol: drain stocks on resize limit >>>>>=20 >>>>> Not sure if they would help out. >>>>=20 >>>> These are all in 4.20, which is tested but not helpful. >>>>=20 >>>> Fam