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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,UNPARSEABLE_RELAY,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 2F837C433E1 for ; Tue, 11 Aug 2020 08:23:07 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D7D5E206DA for ; Tue, 11 Aug 2020 08:23:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D7D5E206DA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 34AE56B0005; Tue, 11 Aug 2020 04:23:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2D6676B0006; Tue, 11 Aug 2020 04:23:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 19C8F6B0007; Tue, 11 Aug 2020 04:23:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0021.hostedemail.com [216.40.44.21]) by kanga.kvack.org (Postfix) with ESMTP id F42366B0005 for ; Tue, 11 Aug 2020 04:23:05 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id AF1C48248047 for ; Tue, 11 Aug 2020 08:23:05 +0000 (UTC) X-FDA: 77137597530.20.soup71_001274b26fe1 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin20.hostedemail.com (Postfix) with ESMTP id 8153D180C07AB for ; Tue, 11 Aug 2020 08:23:05 +0000 (UTC) X-HE-Tag: soup71_001274b26fe1 X-Filterd-Recvd-Size: 5861 Received: from out30-43.freemail.mail.aliyun.com (out30-43.freemail.mail.aliyun.com [115.124.30.43]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Tue, 11 Aug 2020 08:23:03 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R101e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07425;MF=alex.shi@linux.alibaba.com;NM=1;PH=DS;RN=19;SR=0;TI=SMTPD_---0U5S3WRW_1597134176; Received: from IT-FVFX43SYHV2H.local(mailfrom:alex.shi@linux.alibaba.com fp:SMTPD_---0U5S3WRW_1597134176) by smtp.aliyun-inc.com(127.0.0.1); Tue, 11 Aug 2020 16:22:57 +0800 Subject: Re: [PATCH v17 14/21] mm/compaction: do page isolation first in compaction To: Alexander Duyck Cc: Andrew Morton , Mel Gorman , Tejun Heo , Hugh Dickins , Konstantin Khlebnikov , Daniel Jordan , Yang Shi , Matthew Wilcox , Johannes Weiner , kbuild test robot , linux-mm , LKML , cgroups@vger.kernel.org, Shakeel Butt , Joonsoo Kim , Wei Yang , "Kirill A. Shutemov" , Rong Chen References: <1595681998-19193-1-git-send-email-alex.shi@linux.alibaba.com> <1595681998-19193-15-git-send-email-alex.shi@linux.alibaba.com> <241ca157-104f-4f0d-7d5b-de394443788d@linux.alibaba.com> <8dbd004e-8eba-f1ec-a5eb-5dc551978936@linux.alibaba.com> From: Alex Shi Message-ID: Date: Tue, 11 Aug 2020 16:22:27 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 X-Rspamd-Queue-Id: 8153D180C07AB X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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: =E5=9C=A8 2020/8/10 =E4=B8=8B=E5=8D=8810:41, Alexander Duyck =E5=86=99=E9= =81=93: > On Mon, Aug 10, 2020 at 6:10 AM Alex Shi w= rote: >> >> >> >> =E5=9C=A8 2020/8/7 =E4=B8=8B=E5=8D=8810:51, Alexander Duyck =E5=86=99=E9= =81=93: >>> I wonder if this entire section shouldn't be restructured. This is th= e >>> only spot I can see where we are resetting the LRU flag instead of >>> pulling the page from the LRU list with the lock held. Looking over >>> the code it seems like something like that should be possible. I am >>> not sure the LRU lock is really protecting us in either the >>> PageCompound check nor the skip bits. It seems like holding a >>> reference on the page should prevent it from switching between >>> compound or not, and the skip bits are per pageblock with the LRU bit= s >>> being per node/memcg which I would think implies that we could have >>> multiple LRU locks that could apply to a single skip bit. >> >> Hi Alexander, >> >> I don't find problem yet on compound or skip bit usage. Would you clar= ify the >> issue do you concerned? >> >> Thanks! >=20 > The point I was getting at is that the LRU lock is being used to > protect these and with your changes I don't think that makes sense > anymore. >=20 > The skip bits are per-pageblock bits. With your change the LRU lock is > now per memcg first and then per node. As such I do not believe it > really provides any sort of exclusive access to the skip bits. I still > have to look into this more, but it seems like you need a lock per > either section or zone that can be used to protect those bits and deal > with this sooner rather than waiting until you have found an LRU page. > The one part that is confusing though is that the definition of the > skip bits seems to call out that they are a hint since they are not > protected by a lock, but that is exactly what has been happening here. >=20 The skip bits are safe here, since even it race with other skip action, It will still skip out. The skip action is try not to compaction too much= , not a exclusive action needs avoid race. > The point I was getting at with the PageCompound check is that instead > of needing the LRU lock you should be able to look at PageCompound as > soon as you call get_page_unless_zero() and preempt the need to set > the LRU bit again. Instead of trying to rely on the LRU lock to > guarantee that the page hasn't been merged you could just rely on the > fact that you are holding a reference to it so it isn't going to > switch between being compound or order 0 since it cannot be freed. It > spoils the idea I originally had of combining the logic for > get_page_unless_zero and TestClearPageLRU into a single function, but > the advantage is you aren't clearing the LRU flag unless you are > actually going to pull the page from the LRU list. Sorry, I still can not follow you here. Compound code part is unchanged and follow the original logical. So would you like to pose a new code to see if its works? Thanks Alex >=20 > My main worry is that this is the one spot where we appear to be > clearing the LRU bit without ever actually pulling the page off of the > LRU list, and I am thinking we would be better served by addressing > the skip and PageCompound checks earlier rather than adding code to > set the bit again if either of those cases are encountered. This way > we don't pseudo-pin pages in the LRU if they are compound or supposed > to be skipped. >=20 > Thanks. >=20 > - Alex >=20