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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AB01EC433EF for ; Wed, 11 May 2022 18:10:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346089AbiEKSKP (ORCPT ); Wed, 11 May 2022 14:10:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42976 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233707AbiEKSKJ (ORCPT ); Wed, 11 May 2022 14:10:09 -0400 Received: from out2.migadu.com (out2.migadu.com [IPv6:2001:41d0:2:aacc::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2BD25E44C3; Wed, 11 May 2022 11:10:08 -0700 (PDT) Date: Wed, 11 May 2022 11:10:01 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1652292606; 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: in-reply-to:in-reply-to:references:references; bh=SgiEqe1W62i2WZKOS/4pyIuMIMG49SfWBj1MxBbC8vw=; b=umNqkvHUDbWe7akLjEuSDT3lOZjXZR08i0ks+6RB50MqFB/7NqnfYPgVUGtdjALN+NZVSp xJfFD1s1kIVcZlRlL3x97QTgCtnNcYkL9bGOs/jFGALgEX2RNRly6lJBmiy1yS06emoKJB Nc7S8sko/nGpYiNszr2ILHKikNJKDY4= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Roman Gushchin To: Michal =?iso-8859-1?Q?Koutn=FD?= Cc: Vasily Averin , Vlastimil Babka , Shakeel Butt , kernel@openvz.org, Florian Westphal , linux-kernel@vger.kernel.org, Michal Hocko , cgroups@vger.kernel.org, Greg Kroah-Hartman , Tejun Heo Subject: Re: kernfs memcg accounting Message-ID: References: <7e867cb0-89d6-402c-33d2-9b9ba0ba1523@openvz.org> <20220427140153.GC9823@blackbody.suse.cz> <7509fa9f-9d15-2f29-cb2f-ac0e8d99a948@openvz.org> <52a9f35b-458b-44c4-7fc8-d05c8db0c73f@openvz.org> <20220511163439.GD24172@blackbody.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220511163439.GD24172@blackbody.suse.cz> X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 11, 2022 at 06:34:39PM +0200, Michal Koutny wrote: > On Tue, May 10, 2022 at 08:06:24PM -0700, Roman Gushchin wrote: > > My primary goal was to apply the memory pressure on memory cgroups with a lot > > of (dying) children cgroups. On a multi-cpu machine a memory cgroup structure > > is way larger than a page, so a cgroup which looks small can be really large > > if we calculate the amount of memory taken by all children memcg internals. > > > > Applying this pressure to another cgroup (e.g. the one which contains systemd) > > doesn't help to reclaim any pages which are pinning the dying cgroups. > > Just a note -- this another usecase of cgroups created from within the > subtree (e.g. a container). I agree that cgroup-manager/systemd case is > also valid (as dying memcgs may accumulate after a restart). > > memcgs with their retained state with footprint are special. > > > For other controllers (maybe blkcg aside, idk) it shouldn't matter, because > > there is no such problem there. > > > > For consistency reasons I'd suggest to charge all *large* allocations > > (e.g. percpu) to the parent cgroup. Small allocations can be ignored. > > Strictly speaking, this would mean that any controller would have on > implicit dependency on the memory controller (such as io controller > has). > In the extreme case even controller-less hierarchy would have such a > requirement (for precise kernfs_node accounting). > Such a dependency is not enforceable on v1 (with various topologies of > different hierarchies). > > Although, I initially favored the consistency with memory controller too, > I think it's simpler to charge to the creator's memcg to achieve > consistency across v1 and v2 :-) Ok, v1/v2 consistency is a valid point. As I said, I'm fine with both options, it shouldn't matter that much for anything except the memory controller: cgroup internal objects are not that large and the total memory footprint is usually small unless we have a lot of (dying) sub-cgroups. From my experience no other controllers should be affected (blkcg was affected due to a cgwb reference, but should be fine now), so it's not an issue at all. Thanks!