From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Gushchin Subject: Re: [PATCH v2 0/5] Introduce memcg_stock_pcp remote draining Date: Thu, 26 Jan 2023 15:12:35 -0800 Message-ID: References: <20230125073502.743446-1-leobras@redhat.com> <9e61ab53e1419a144f774b95230b789244895424.camel@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1674774772; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=n7M1bfJLC4Rcsy/Y/usaqBvuQAjlpdOFXty5eUdj7PU=; b=paF0N/iKfvlcN9yEEM/b2TNNUDXisDdGcz0WAIRf6cjejS0WzLPSni7TNGvbneMeKyzDyj Lebr5WBZ2hHo/G7w6N+e4AuL7TZD6obbBxM+8Sp8zk0464GNq3oxk2qH50NdUF/jGCuI0o X0rTkDGfQwBBfQ8Dxmnb/f/xbQMWc8E= Content-Disposition: inline In-Reply-To: List-ID: Content-Type: text/plain; charset="iso-8859-1" To: Michal Hocko Cc: Marcelo Tosatti , Leonardo =?iso-8859-1?Q?Br=E1s?= , Johannes Weiner , Shakeel Butt , Muchun Song , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, Jan 26, 2023 at 08:41:34AM +0100, Michal Hocko wrote: > On Wed 25-01-23 15:14:48, Roman Gushchin wrote: > > On Wed, Jan 25, 2023 at 03:22:00PM -0300, Marcelo Tosatti wrote: > > > On Wed, Jan 25, 2023 at 08:06:46AM -0300, Leonardo Br=E1s wrote: > > > > On Wed, 2023-01-25 at 09:33 +0100, Michal Hocko wrote: > > > > > On Wed 25-01-23 04:34:57, Leonardo Bras wrote: > > > > > > Disclaimer: > > > > > > a - The cover letter got bigger than expected, so I had to spli= t it in > > > > > > sections to better organize myself. I am not very confortab= le with it. > > > > > > b - Performance numbers below did not include patch 5/5 (Remove= flags > > > > > > from memcg_stock_pcp), which could further improve performa= nce for > > > > > > drain_all_stock(), but I could only notice the optimization= at the > > > > > > last minute. > > > > > >=20 > > > > > >=20 > > > > > > 0 - Motivation: > > > > > > On current codebase, when drain_all_stock() is ran, it will sch= edule a > > > > > > drain_local_stock() for each cpu that has a percpu stock associ= ated with a > > > > > > descendant of a given root_memcg. > >=20 > > Do you know what caused those drain_all_stock() calls? I wonder if we s= hould look > > into why we have many of them and whether we really need them? > >=20 > > It's either some user's actions (e.g. reducing memory.max), either some= memcg > > is entering pre-oom conditions. In the latter case a lot of drain calls= can be > > scheduled without a good reason (assuming the cgroup contain multiple t= asks running > > on multiple cpus). >=20 > I believe I've never got a specific answer to that. We > have discussed that in the previous version submission > (20221102020243.522358-1-leobras@redhat.com and specifically > Y2TQLavnLVd4qHMT@dhcp22.suse.cz). Leonardo has mentioned a mix of RT and > isolcpus. I was wondering about using memcgs in RT workloads because > that just sounds weird but let's say this is the case indeed. Then an RT > task or whatever task that is running on an isolated cpu can have pcp > charges. >=20 > > Essentially each cpu will try to grab the remains of the memory quota > > and move it locally. I wonder in such circumstances if we need to disab= le the pcp-caching > > on per-cgroup basis. >=20 > I think it would be more than sufficient to disable pcp charging on an > isolated cpu. It might have significant performance consequences. I'd rather opt out of stock draining for isolated cpus: it might slightly r= educe the accuracy of memory limits and slightly increase the memory footprint (a= ll those dying memcgs...), but the impact will be limited. Actually it is limi= ted by the number of cpus. > This is not a per memcg property. Sure, my point was that in pre-oom condition several cpus might try to cons= olidate the remains of the memory quota, actually working against each other. Separ= ate issue, which might be a reason why there are many flush attempts in the case we di= scuss. Thanks!