From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt1-f199.google.com (mail-qt1-f199.google.com [209.85.160.199]) by kanga.kvack.org (Postfix) with ESMTP id 147528E0002 for ; Wed, 16 Jan 2019 16:06:27 -0500 (EST) Received: by mail-qt1-f199.google.com with SMTP id 41so6826803qto.17 for ; Wed, 16 Jan 2019 13:06:27 -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 20sor90999726qvz.9.2019.01.16.13.06.25 for (Google Transport Security); Wed, 16 Jan 2019 13:06:25 -0800 (PST) MIME-Version: 1.0 References: <15614FDC-198E-449B-BFAF-B00D6EF61155@bytedance.com> <97A4C2CA-97BA-46DB-964A-E44410BB1730@bytedance.com> <9B56B884-8FDD-4BB5-A6CA-AD7F84397039@bytedance.com> In-Reply-To: From: Yang Shi Date: Wed, 16 Jan 2019 13:06:14 -0800 Message-ID: Subject: Re: memory cgroup pagecache and inode problem Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Fam Zheng Cc: 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 Tue, Jan 15, 2019 at 7:52 PM Fam Zheng wrote= : > > > > > On Jan 16, 2019, at 08:50, Yang Shi wrote: > > > > On Thu, Jan 10, 2019 at 12:30 AM Fam Zheng = wrote: > >> > >> > >> > >>> On Jan 10, 2019, at 13:36, Yang Shi wrote: > >>> > >>> On Sun, Jan 6, 2019 at 9:10 PM Fam Zheng = wrote: > >>>> > >>>> > >>>> > >>>>> On Jan 5, 2019, at 03:36, Yang Shi wrote: > >>>>> > >>>>> > >>>>> drop_caches would drop all page caches globally. You may not want t= o > >>>>> drop the page caches used by other memcgs. > >>>> > >>>> We=E2=80=99ve tried your async force_empty patch (with a modificatio= n to default it to true to make it transparently enabled for the sake of te= sting), and for the past few days the stale mem cgroups still accumulate, u= p to 40k. > >>>> > >>>> We=E2=80=99ve double checked that the force_empty routines are invok= ed when a mem cgroup is offlined. But this doesn=E2=80=99t look very effect= ive so far. Because, once we do `echo 1 > /proc/sys/vm/drop_caches`, all th= e groups immediately go away. > >>>> > >>>> This is a bit unexpected. > >>>> > >>>> Yang, could you hint what are missing in the force_empty operation, = compared to a blanket drop cache? > >>> > >>> Drop caches does invalidate pages inode by inode. But, memcg > >>> force_empty does call memcg direct reclaim. > >> > >> 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= , > > > > AFAICS, force_empty may unmap pages, but drop_caches doesn't. > > > >> 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? > > > > 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. > > 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=99ll do m= ore tracing (to have a better understanding of the issue) and post the find= ings and/or the patch later. Thanks. 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. Yang > > Fam > > > > > Yang > > > >> > >> > >>> > >>> Offlined memcgs will not go away if there is still page charged. Mayb= e > >>> relate to per cpu memcg stock. I recall there are some commits which > >>> do solve the per cpu page counter cache problem. > >>> > >>> 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 > >>> > >>> Not sure if they would help out. > >> > >> These are all in 4.20, which is tested but not helpful. > >> > >> Fam >