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 X-Spam-Level: X-Spam-Status: No, score=-3.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 82864C43387 for ; Tue, 15 Jan 2019 07:25:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 50CE220873 for ; Tue, 15 Jan 2019 07:25:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1547537157; bh=d2SNeEmwummT8hH3SF8+VtwoLO6nLeQjw/O4Ivaxx5E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=JrX/6AjkM5MAfOnaUhgEQCpMRdBrTrYBEGqHYhfYR08Ln8tYMoM6hx31sgOuhciHp SdjRItwc9SH8NR60x4PeIn6NzaWJOl0P4XaSFZPNnZPUhZT8YTTwnMsEESXVFUoFwc 3xAyALtM204IFqcQOc+AuXla3eGuxczvXta6Mz6s= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728131AbfAOHZz (ORCPT ); Tue, 15 Jan 2019 02:25:55 -0500 Received: from mx2.suse.de ([195.135.220.15]:39634 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727273AbfAOHZz (ORCPT ); Tue, 15 Jan 2019 02:25:55 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 25FDCAC8A; Tue, 15 Jan 2019 07:25:53 +0000 (UTC) Date: Tue, 15 Jan 2019 08:25:51 +0100 From: Michal Hocko To: Shakeel Butt Cc: Johannes Weiner , Andrew Morton , Vladimir Davydov , Cgroups , Linux MM , LKML Subject: Re: [PATCH v3] memcg: schedule high reclaim for remote memcgs on high_work Message-ID: <20190115072551.GO21345@dhcp22.suse.cz> References: <20190110174432.82064-1-shakeelb@google.com> <20190111205948.GA4591@cmpxchg.org> <20190113183402.GD1578@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 14-01-19 12:18:07, Shakeel Butt wrote: > On Sun, Jan 13, 2019 at 10:34 AM Michal Hocko wrote: > > > > On Fri 11-01-19 14:54:32, Shakeel Butt wrote: > > > Hi Johannes, > > > > > > On Fri, Jan 11, 2019 at 12:59 PM Johannes Weiner wrote: > > > > > > > > Hi Shakeel, > > > > > > > > On Thu, Jan 10, 2019 at 09:44:32AM -0800, Shakeel Butt wrote: > > > > > If a memcg is over high limit, memory reclaim is scheduled to run on > > > > > return-to-userland. However it is assumed that the memcg is the current > > > > > process's memcg. With remote memcg charging for kmem or swapping in a > > > > > page charged to remote memcg, current process can trigger reclaim on > > > > > remote memcg. So, schduling reclaim on return-to-userland for remote > > > > > memcgs will ignore the high reclaim altogether. So, record the memcg > > > > > needing high reclaim and trigger high reclaim for that memcg on > > > > > return-to-userland. However if the memcg is already recorded for high > > > > > reclaim and the recorded memcg is not the descendant of the the memcg > > > > > needing high reclaim, punt the high reclaim to the work queue. > > > > > > > > The idea behind remote charging is that the thread allocating the > > > > memory is not responsible for that memory, but a different cgroup > > > > is. Why would the same thread then have to work off any high excess > > > > this could produce in that unrelated group? > > > > > > > > Say you have a inotify/dnotify listener that is restricted in its > > > > memory use - now everybody sending notification events from outside > > > > that listener's group would get throttled on a cgroup over which it > > > > has no control. That sounds like a recipe for priority inversions. > > > > > > > > It seems to me we should only do reclaim-on-return when current is in > > > > the ill-behaved cgroup, and punt everything else - interrupts and > > > > remote charges - to the workqueue. > > > > > > This is what v1 of this patch was doing but Michal suggested to do > > > what this version is doing. Michal's argument was that the current is > > > already charging and maybe reclaiming a remote memcg then why not do > > > the high excess reclaim as well. > > > > Johannes has a good point about the priority inversion problems which I > > haven't thought about. > > > > > Personally I don't have any strong opinion either way. What I actually > > > wanted was to punt this high reclaim to some process in that remote > > > memcg. However I didn't explore much on that direction thinking if > > > that complexity is worth it. Maybe I should at least explore it, so, > > > we can compare the solutions. What do you think? > > > > My question would be whether we really care all that much. Do we know of > > workloads which would generate a large high limit excess? > > > > The current semantics of memory.high is that it can be breached under > extreme conditions. However any workload where memory.high is used and > a lot of remote memcg charging happens (inotify/dnotify example given > by Johannes or swapping in tmpfs file or shared memory region) the > memory.high breach will become common. This is exactly what I am asking about. Is this something that can happen easily? Remote charges on themselves should be rare, no? -- Michal Hocko SUSE Labs