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=-5.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 56BB7C433E0 for ; Thu, 25 Feb 2021 23:09:26 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CFF3E64EF5 for ; Thu, 25 Feb 2021 23:09:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CFF3E64EF5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 50FC06B0005; Thu, 25 Feb 2021 17:49:07 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 497D46B0006; Thu, 25 Feb 2021 17:49:07 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3AEC06B006C; Thu, 25 Feb 2021 17:49:07 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0028.hostedemail.com [216.40.44.28]) by kanga.kvack.org (Postfix) with ESMTP id 273FE6B0005 for ; Thu, 25 Feb 2021 17:49:07 -0500 (EST) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E8EFAF043 for ; Thu, 25 Feb 2021 22:49:06 +0000 (UTC) X-FDA: 77858282292.09.D1745D5 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by imf22.hostedemail.com (Postfix) with ESMTP id 4254CC0007D0 for ; Thu, 25 Feb 2021 22:49:02 +0000 (UTC) IronPort-SDR: yjA8I+hmkj8MoxbqJfmnWyMvkeg8bh6Vqk+V5WAJV7Vx6rsoOY/dltYWpi6kCXxbfLRqMRP8im b2W354f1jkxw== X-IronPort-AV: E=McAfee;i="6000,8403,9906"; a="185755598" X-IronPort-AV: E=Sophos;i="5.81,207,1610438400"; d="scan'208";a="185755598" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Feb 2021 14:49:03 -0800 IronPort-SDR: iNQrhR4B49D66thWy+kAZeBWhban/MHq1DSL3qHgMM8rR/clwTk3ySMQQF0TJ3oixjADsJcSNG AfByzWW6o0dQ== X-IronPort-AV: E=Sophos;i="5.81,207,1610438400"; d="scan'208";a="442790842" Received: from schen9-mobl.amr.corp.intel.com ([10.254.86.33]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Feb 2021 14:49:03 -0800 Subject: Re: [PATCH v2 2/3] mm: Force update of mem cgroup soft limit tree on usage excess To: Michal Hocko Cc: Andrew Morton , Johannes Weiner , Vladimir Davydov , Dave Hansen , Ying Huang , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org References: <06f1f92f1f7d4e57c4e20c97f435252c16c60a27.1613584277.git.tim.c.chen@linux.intel.com> <884d7559-e118-3773-351d-84c02642ca96@linux.intel.com> From: Tim Chen Message-ID: Date: Thu, 25 Feb 2021 14:48:58 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 4254CC0007D0 X-Stat-Signature: 9iotnm5mf4gk77hxmfdh11x5zi95i3rr Received-SPF: none (linux.intel.com>: No applicable sender policy available) receiver=imf22; identity=mailfrom; envelope-from=""; helo=mga03.intel.com; client-ip=134.134.136.65 X-HE-DKIM-Result: none/none X-HE-Tag: 1614293342-832722 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 2/24/21 3:53 AM, Michal Hocko wrote: > On Mon 22-02-21 11:48:37, Tim Chen wrote: >> >> >> On 2/22/21 11:09 AM, Michal Hocko wrote: >> >>>> >>>> I actually have tried adjusting the threshold but found that it doesn't work well for >>>> the case with unenven memory access frequency between cgroups. The soft >>>> limit for the low memory event cgroup could creep up quite a lot, exceeding >>>> the soft limit by hundreds of MB, even >>>> if I drop the SOFTLIMIT_EVENTS_TARGET from 1024 to something like 8. >>> >>> What was the underlying reason? Higher order allocations? >>> >> >> Not high order allocation. >> >> The reason was because the run away memcg asks for memory much less often, compared >> to the other memcgs in the system. So it escapes the sampling update and >> was not put onto the tree and exceeds the soft limit >> pretty badly. Even if it was put onto the tree and gets page reclaimed below the >> limit, it could escape the sampling the next time it exceeds the soft limit. > > I am sorry but I really do not follow. Maybe I am missing something > obvious but the the rate of events (charge/uncharge) shouldn't be really > important. There is no way to exceed the limit without charging memory > (either a new or via task migration in v1 and immigrate_on_move). If you > have SOFTLIMIT_EVENTS_TARGET 8 then you should be 128 * 8 events to > re-evaluate. Huge pages can make the runaway much bigger but how it > would be possible to runaway outside of that bound. Michal, Let's take an extreme case where memcg 1 always generate the first event and memcg 2 generates the rest of 128*8-1 events and the pattern repeat. The update tree happens on the 128*8th event so memcg 1 did not trigger update tree. In this case we will keep missing memcg 1's event and not put memcg 1 on the tree. Something like this pattern of memory events cg1 cg2 cg2 cg2 ....cg2 cg1 cg2 cg2 cg2....cg2 cg1 cg2 ..... ^ ^ update tree update tree Of course in real life the update events are random in nature. However, due to the low occurrence of memcg 1 event, we can miss updating it for a long time due to its lower probability of occurrence. > > Btw. do we really need SOFTLIMIT_EVENTS_TARGET at all? Why cannot we > just stick with a single threshold? mem_cgroup_update_tree can be made > a effectivelly a noop when there is no soft limit in place so overhead > shouldn't matter for the vast majority of workloads. > I think there are two limits because the original code wants memc_cgroup_threshold to be updated more frequently than the soft_limit_tree. The soft limit tree update is more costly. Tim