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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 48113C433DF for ; Thu, 28 May 2020 16:48:52 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0B85D2075A for ; Thu, 28 May 2020 16:48:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chrisdown.name header.i=@chrisdown.name header.b="PPb3j7a/" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0B85D2075A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chrisdown.name Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 89FD78001A; Thu, 28 May 2020 12:48:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 84EF880010; Thu, 28 May 2020 12:48:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 73CDC8001A; Thu, 28 May 2020 12:48:51 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 5963780010 for ; Thu, 28 May 2020 12:48:51 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 0B0A08248D51 for ; Thu, 28 May 2020 16:48:51 +0000 (UTC) X-FDA: 76866712062.07.basin52_4d383a700a44b Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin07.hostedemail.com (Postfix) with ESMTP id DE0CD1803FFD1 for ; Thu, 28 May 2020 16:48:50 +0000 (UTC) X-HE-Tag: basin52_4d383a700a44b X-Filterd-Recvd-Size: 6092 Received: from mail-wm1-f67.google.com (mail-wm1-f67.google.com [209.85.128.67]) by imf30.hostedemail.com (Postfix) with ESMTP for ; Thu, 28 May 2020 16:48:50 +0000 (UTC) Received: by mail-wm1-f67.google.com with SMTP id v19so4002432wmj.0 for ; Thu, 28 May 2020 09:48:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chrisdown.name; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=UwZ28g34UZ/LmYps/esI5h2JZjKeclqR/inpTX02z2o=; b=PPb3j7a/BdD86VI8igVSltNvHQ9B8pjLLH1ePEwa/baG3Wzmss76Lv0gRQbqiB0y7I qB3fSv9TLfHEKw23N/5h80TiBDGczfNsmJpY+OMnOWzCIfO1yGUMNJi8SGt8vStQ6HYl zOW8eKaK+Jq3r13HH3nV3qAD0HpX1p6KWe31I= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=UwZ28g34UZ/LmYps/esI5h2JZjKeclqR/inpTX02z2o=; b=hscMmuMtbW3nMfDQ/qWK8X/BhMHWxsws75NVJuuaOzR3JuN6WdTRtQMEL3mh3LkkRl P26AWRWCC6uQhodb2EUu4UQGXkjtL0afVq7EoPaB3f0/JGS4HrwEpNqIvLHt/nPEoFyh YHu36pNmPYkSZUYX0jLHM1Zqzcql+S+zIgAE86ZM34JdyEWntqnwcGHL/bMTaQpFO6X9 e+3E6tcZjdQjIdMqsSHQzDwKBVDk7N8BDgFjmPSqUAEsAIBkY07W77JleeMuhfiSuASa +puHlaTvPwjjiwNjKm9ltedOzyQohbBcZKdgrEtN1uEPZ3MnRPolC22LpleQ2crycIw6 dE2Q== X-Gm-Message-State: AOAM533pX83IyV/ApGi98LnUV8XEyyQ6Vs7rd+JSzlHhcFZMzEn0y/SV mHu7V0OGvDvPERXH+Ob0CUog3Q== X-Google-Smtp-Source: ABdhPJx2lEUjIyLYkOhiyOkgO1n10vkCe0XPXbDohjqU2El6rgKvXLDbPYgyqKrqd2CxBujY0bcjUQ== X-Received: by 2002:a1c:810a:: with SMTP id c10mr4180798wmd.107.1590684529184; Thu, 28 May 2020 09:48:49 -0700 (PDT) Received: from localhost ([2620:10d:c093:400::5:d125]) by smtp.gmail.com with ESMTPSA id u13sm6429380wrp.53.2020.05.28.09.48.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 May 2020 09:48:48 -0700 (PDT) Date: Thu, 28 May 2020 17:48:48 +0100 From: Chris Down To: Michal Hocko Cc: Johannes Weiner , Andrew Morton , Tejun Heo , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH] mm, memcg: reclaim more aggressively before high allocator throttling Message-ID: <20200528164848.GB839178@chrisdown.name> References: <20200520165131.GB630613@cmpxchg.org> <20200520170430.GG6462@dhcp22.suse.cz> <20200520175135.GA793901@cmpxchg.org> <20200521073245.GI6462@dhcp22.suse.cz> <20200521135152.GA810429@cmpxchg.org> <20200521143515.GU6462@dhcp22.suse.cz> <20200521163833.GA813446@cmpxchg.org> <20200521173701.GX6462@dhcp22.suse.cz> <20200521184505.GA815980@cmpxchg.org> <20200528163101.GJ27484@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20200528163101.GJ27484@dhcp22.suse.cz> User-Agent: Mutt/1.14.2 (2020-05-25) X-Rspamd-Queue-Id: DE0CD1803FFD1 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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: Michal Hocko writes: >> We send a simple bug fix: bring this instance of reclaim in line with >> how everybody else is using the reclaim API, to meet the semantics as >> they are intendend and documented. > >Here is where we are not on the same page though. Once you have identified >that the main problem is that the reclaim fails too early to meet the >target then the fix would be to enforce that target. I have asked why >this hasn't been done and haven't got any real answer for that. Instead >what you call "a simple bug fix" has larger consequences which are not >really explained in the changelog and they are also not really trivial >to see. If the changelog explicitly stated that the proportional memory >reclaim is not sufficient because XYZ and the implementation has been >changed to instead meet the high limit target then this would be a >completely different story and I believe we could have saved some >discussion. I agree that the changelog can be made more clear. Any objection if I send v2 with changelog changes to that effect, then? :-) >> And somehow this is controversial, and we're just changing around user >> promises as we see fit for our particular usecase? >> >> I don't even understand how the supposed alternate semantics you read >> between the lines in the documentation would make for a useful >> feature: It may fail to contain a group of offending tasks to the >> configured limit, but it will be fair to those tasks while doing so? >> >> > But if your really want to push this through then let's do it >> > properly at least. memcg->memcg_nr_pages_over_high has only very >> > vague meaning if the reclaim target is the high limit. >> >> task->memcg_nr_pages_over_high is not vague, it's a best-effort >> mechanism to distribute fairness. It's the current task's share of the >> cgroup's overage, and it allows us in the majority of situations to >> distribute reclaim work and sleeps in proportion to how much the task >> is actually at fault. > >Agreed. But this stops being the case as soon as the reclaim target has >been reached and new reclaim attempts are enforced because the memcg is >still above the high limit. Because then you have a completely different >reclaim target - get down to the limit. This would be especially visible >with a large memcg_nr_pages_over_high which could even lead to an over >reclaim. We actually over reclaim even before this patch -- this patch doesn't bring much new in that regard. Tracing try_to_free_pages for a cgroup at the memory.high threshold shows that before this change, we sometimes even reclaim on the order of twice the number of pages requested. For example, I see cases where we requested 1000 pages to be reclaimed, but end up reclaiming 2000 in a single reclaim attempt.