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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED 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 B8C7CC43387 for ; Wed, 9 Jan 2019 17:58:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9571920685 for ; Wed, 9 Jan 2019 17:58:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727214AbfAIR6R (ORCPT ); Wed, 9 Jan 2019 12:58:17 -0500 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:41801 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727129AbfAIR6Q (ORCPT ); Wed, 9 Jan 2019 12:58:16 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07487;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0THtuaGf_1547056537; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0THtuaGf_1547056537) by smtp.aliyun-inc.com(127.0.0.1); Thu, 10 Jan 2019 01:55:40 +0800 Subject: Re: [v2 PATCH 2/5] mm: memcontrol: do not try to do swap when force empty To: Shakeel Butt Cc: Michal Hocko , Johannes Weiner , Andrew Morton , Linux MM , LKML References: <1546647560-40026-1-git-send-email-yang.shi@linux.alibaba.com> <1546647560-40026-3-git-send-email-yang.shi@linux.alibaba.com> From: Yang Shi Message-ID: Date: Wed, 9 Jan 2019 09:55:34 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/4/19 4:43 PM, Shakeel Butt wrote: > On Fri, Jan 4, 2019 at 4:21 PM Yang Shi wrote: >> The typical usecase of force empty is to try to reclaim as much as >> possible memory before offlining a memcg. Since there should be no >> attached tasks to offlining memcg, the tasks anonymous pages would have >> already been freed or uncharged. Even though anonymous pages get >> swapped out, but they still get charged to swap space. So, it sounds >> pointless to do swap for force empty. >> >> I tried to dig into the history of this, it was introduced by >> commit 8c7c6e34a125 ("memcg: mem+swap controller core"), but there is >> not any clue about why it was done so at the first place. >> >> The below simple test script shows slight file cache reclaim improvement >> when swap is on. >> >> echo 3 > /proc/sys/vm/drop_caches >> mkdir /sys/fs/cgroup/memory/test >> echo 30 > /sys/fs/cgroup/memory/test/memory.swappiness >> echo $$ >/sys/fs/cgroup/memory/test/cgroup.procs >> cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' >> dd if=/dev/zero of=/mnt/test bs=1M count=1024 >> ping localhost > /dev/null & >> echo 1 > /sys/fs/cgroup/memory/test/memory.force_empty >> killall ping >> echo $$ >/sys/fs/cgroup/memory/cgroup.procs >> cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' >> rmdir /sys/fs/cgroup/memory/test >> cat /proc/meminfo | grep ^Cached|awk -F" " '{print $2}' >> >> The number of page cache is: >> w/o w/ >> before force empty 1088792 1088784 >> after force empty 41492 39428 >> reclaimed 1047300 1049356 >> >> Without doing swap, force empty can reclaim 2MB more memory in 1GB page >> cache. >> >> Cc: Michal Hocko >> Cc: Johannes Weiner >> Signed-off-by: Yang Shi >> --- >> mm/memcontrol.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index af7f18b..75208a2 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -2895,7 +2895,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup *memcg) >> return -EINTR; >> >> progress = try_to_free_mem_cgroup_pages(memcg, 1, >> - GFP_KERNEL, true); >> + GFP_KERNEL, false); > I think we agreed not to change the behavior of force_empty. You can > customize 'force_empty on wipe_on_offline' to not swapout. OK, will keep force_empty intact. Thanks, Yang > >> if (!progress) { >> nr_retries--; >> /* maybe some writeback is necessary */ >> -- >> 1.8.3.1 >>