From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f198.google.com (mail-pf1-f198.google.com [209.85.210.198]) by kanga.kvack.org (Postfix) with ESMTP id 8DDEF8E009D for ; Wed, 9 Jan 2019 12:58:05 -0500 (EST) Received: by mail-pf1-f198.google.com with SMTP id 68so5759661pfr.6 for ; Wed, 09 Jan 2019 09:58:05 -0800 (PST) Received: from out30-132.freemail.mail.aliyun.com (out30-132.freemail.mail.aliyun.com. [115.124.30.132]) by mx.google.com with ESMTPS id 61si19814262plz.117.2019.01.09.09.58.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Jan 2019 09:58:04 -0800 (PST) Subject: Re: [v2 PATCH 2/5] mm: memcontrol: do not try to do swap when force empty 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 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: owner-linux-mm@kvack.org List-ID: To: Shakeel Butt Cc: Michal Hocko , Johannes Weiner , Andrew Morton , Linux MM , LKML 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 >>