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=-6.6 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 D648AC433E1 for ; Thu, 20 Aug 2020 15:22:04 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A1B2C206DA for ; Thu, 20 Aug 2020 15:22:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A1B2C206DA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 24BFC8D0009; 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Thu, 20 Aug 2020 15:21:57 +0000 (UTC) IronPort-SDR: tv4FFw4W0Vs1jBsb1+dCxpdm4FqJ3WEd0r7QDul5PjQiHIMxS/AnAPG0A1WLwMBYNQLOQveJG8 HdM+cD1B6wPA== X-IronPort-AV: E=McAfee;i="6000,8403,9718"; a="135383299" X-IronPort-AV: E=Sophos;i="5.76,333,1592895600"; d="scan'208";a="135383299" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Aug 2020 08:21:56 -0700 IronPort-SDR: Uaqrd/K30h5wHd4hAWWBSBxaz5iW8psIfFE0swpnJhZezQjFqTuwBal0dg/2RfKBcsYsEXqlWe nVG01Lo2vUBQ== X-IronPort-AV: E=Sophos;i="5.76,333,1592895600"; d="scan'208";a="327462679" Received: from nguerr1-mobl1.amr.corp.intel.com (HELO [10.251.25.200]) ([10.251.25.200]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Aug 2020 08:21:55 -0700 Subject: Re: [RFC][PATCH 5/9] mm/migrate: demote pages during reclaim To: "Huang, Ying" , Dave Hansen Cc: linux-kernel@vger.kernel.org, yang.shi@linux.alibaba.com, rientjes@google.com, dan.j.williams@intel.com, Linux-MM References: <20200818184122.29C415DF@viggo.jf.intel.com> <20200818184131.C972AFCC@viggo.jf.intel.com> <87lfi9wxk9.fsf@yhuang-dev.intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <87lfi9wxk9.fsf@yhuang-dev.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US X-Rspamd-Queue-Id: 919D43D678 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 Content-Transfer-Encoding: quoted-printable 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 8/20/20 1:06 AM, Huang, Ying wrote: >> + /* Migrate pages selected for demotion */ >> + nr_reclaimed +=3D demote_page_list(&ret_pages, &demote_pages, pgdat,= sc); >> + >> pgactivate =3D stat->nr_activate[0] + stat->nr_activate[1]; >> =20 >> mem_cgroup_uncharge_list(&free_pages); >> _ > Generally, it's good to batch the page migration. But one side effect > is that, if the pages are failed to be migrated, they will be placed > back to the LRU list instead of falling back to be reclaimed really. > This may cause some issue in some situation. For example, if there's n= o > enough space in the PMEM (slow) node, so the page migration fails, OOM > may be triggered, because the direct reclaiming on the DRAM (fast) node > may make no progress, while it can reclaim some pages really before. Yes, agreed. There are a couple of ways we could fix this. Instead of splicing 'demote_pages' back into 'ret_pages', we could try to get them back on 'page_list' and goto the beginning on shrink_page_list(). This will probably yield the best behavior, but might be a bit ugly. We could also add a field to 'struct scan_control' and just stop trying to migrate after it has failed one or more times. The trick will be picking a threshold that doesn't mess with either the normal reclaim rate or the migration rate. This is on my list to fix up next.