From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f197.google.com (mail-pg1-f197.google.com [209.85.215.197]) by kanga.kvack.org (Postfix) with ESMTP id BA58E8E00F9 for ; Fri, 4 Jan 2019 19:21:49 -0500 (EST) Received: by mail-pg1-f197.google.com with SMTP id 143so31388638pgc.3 for ; Fri, 04 Jan 2019 16:21:49 -0800 (PST) Received: from out30-130.freemail.mail.aliyun.com (out30-130.freemail.mail.aliyun.com. [115.124.30.130]) by mx.google.com with ESMTPS id 128si11536625pgh.261.2019.01.04.16.21.47 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 04 Jan 2019 16:21:48 -0800 (PST) From: Yang Shi Subject: [v2 PATCH 2/5] mm: memcontrol: do not try to do swap when force empty Date: Sat, 5 Jan 2019 08:19:17 +0800 Message-Id: <1546647560-40026-3-git-send-email-yang.shi@linux.alibaba.com> In-Reply-To: <1546647560-40026-1-git-send-email-yang.shi@linux.alibaba.com> References: <1546647560-40026-1-git-send-email-yang.shi@linux.alibaba.com> Sender: owner-linux-mm@kvack.org List-ID: To: mhocko@suse.com, hannes@cmpxchg.org, shakeelb@google.com, akpm@linux-foundation.org Cc: yang.shi@linux.alibaba.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org 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); if (!progress) { nr_retries--; /* maybe some writeback is necessary */ -- 1.8.3.1