From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id B54FBC433EF for ; Wed, 1 Jun 2022 15:24:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EEEED8D0022; Wed, 1 Jun 2022 11:24:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E9DC98D001C; Wed, 1 Jun 2022 11:24:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DAEA58D0022; Wed, 1 Jun 2022 11:24:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id C63798D001C for ; Wed, 1 Jun 2022 11:24:09 -0400 (EDT) Received: from smtpin05.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 99FF860E31 for ; Wed, 1 Jun 2022 15:24:09 +0000 (UTC) X-FDA: 79530037818.05.624B284 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf02.hostedemail.com (Postfix) with ESMTP id B49388006C for ; Wed, 1 Jun 2022 15:24:03 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 799FB21A8E; Wed, 1 Jun 2022 15:24:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1654097047; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=aXHVZxPrCb1BC4QlFo14+VbIvXvZSlCAD3WV4pOVYmw=; b=T922d8GC3bWNBspwD1NiXwCVli/WrJ0y2/jgveZXBNXPO7O3yjF0tFdgjr+1964bwIrTht lGTss9VOc+v0i3QXzuRV0PR6KVNbLsEyx3g6iGuAJC4CA4ofjdFZabdwmryfiMjhH8Nmz4 e2Wd+pHLq9B9M2wntZflyZkR+kIrBeU= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id D480F2C141; Wed, 1 Jun 2022 15:24:06 +0000 (UTC) Date: Wed, 1 Jun 2022 17:24:06 +0200 From: Michal Hocko To: Roman Gushchin Cc: Michal =?iso-8859-1?Q?Koutn=FD?= , Vasily Averin , Andrew Morton , kernel@openvz.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Shakeel Butt , Vlastimil Babka , Muchun Song , cgroups@vger.kernel.org Subject: Re: [PATCH mm v3 0/9] memcg: accounting for objects allocated by mkdir cgroup Message-ID: References: <3a1d8554-755f-7976-1e00-a0e7fb62c86e@openvz.org> <118bcb39-1281-0d1d-b163-3f6bcc99c3e2@openvz.org> <20220601091543.GA21320@blackbody.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: B49388006C X-Stat-Signature: wkd4otb9jy3xq5nm7eqd9mrpo5yooned X-Rspam-User: Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=T922d8GC; spf=pass (imf02.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-HE-Tag: 1654097043-981969 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed 01-06-22 07:22:05, Roman Gushchin wrote: > On Wed, Jun 01, 2022 at 03:05:34PM +0200, Michal Hocko wrote: > > On Wed 01-06-22 11:32:26, Michal Hocko wrote: > > > On Wed 01-06-22 11:15:43, Michal Koutny wrote: > > > > On Wed, Jun 01, 2022 at 06:43:27AM +0300, Vasily Averin wrote: > > > > > CT-901 /# cat /sys/fs/cgroup/memory/cgroup.subgroups_limit > > > > > 512 > > > > > CT-901 /# echo 3333 > /sys/fs/cgroup/memory/cgroup.subgroups_limit > > > > > -bash: echo: write error: Operation not permitted > > > > > CT-901 /# echo 333 > /sys/fs/cgroup/memory/cgroup.subgroups_limit > > > > > -bash: echo: write error: Operation not permitted > > > > > > > > > > I doubt this way can be accepted in upstream, however for OpenVz > > > > > something like this it is mandatory because it much better > > > > > than nothing. > > > > > > > > Is this customization of yours something like cgroup.max.descendants on > > > > the unified (v2) hierarchy? (Just curious.) > > > > > > > > (It can be made inaccessible from within the subtree either with cgroup > > > > ns or good old FS permissions.) > > > > > > So we already do have a limit to prevent somebody from running away with > > > the number of cgroups. Nice! > > Yes, we do! > > > > I was not aware of that and I guess this > > > looks like the right thing to do. So do we need more control and > > > accounting that this? > > > > I have checked the actual implementation and noticed that cgroups are > > uncharged when offlined (rmdir-ed) which means that an adversary could > > still trick the limit and runaway while still consuming resources. > > > > Roman, I guess the reason for this implementation was to avoid limit to > > trigger on setups with memcgs which can take quite some time to die? > > Would it make sense to make the implementation more strict to really act > > as gate against potential cgroups count runways? > > The reasoning was that in many cases a user can't do much about dying cgroups, > so it's not clear how they should/would handle getting -EAGAIN on creating a > new cgroup (retrying will not help, obviously). Live cgroups can be easily > deleted, dying cgroups - not always. > > I'm not sure about switching the semantics. I'd wait till Muchun's lru page > reparenting will be landed (could be within 1-2 releases, I guess) and then we > can check whether the whole problem is mostly gone. Honestly, I think we might > need to fix few another things, but it might be not that hard (in comparison > to what we already did). OK, thanks for the confirmation! Say we end up mitigating the too-easy-to-linger memcgs long standing issue. Do we still need an extended cgroup data structure accounting? -- Michal Hocko SUSE Labs