From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f197.google.com (mail-pl1-f197.google.com [209.85.214.197]) by kanga.kvack.org (Postfix) with ESMTP id 92E028E0038 for ; Wed, 9 Jan 2019 14:20:04 -0500 (EST) Received: by mail-pl1-f197.google.com with SMTP id 4so4722287plc.5 for ; Wed, 09 Jan 2019 11:20:04 -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 x5si7000951pga.440.2019.01.09.11.20.02 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Jan 2019 11:20:02 -0800 (PST) From: Yang Shi Subject: [v3 PATCH 4/5] mm: memcontrol: bring force_empty into default hierarchy Date: Thu, 10 Jan 2019 03:14:44 +0800 Message-Id: <1547061285-100329-5-git-send-email-yang.shi@linux.alibaba.com> In-Reply-To: <1547061285-100329-1-git-send-email-yang.shi@linux.alibaba.com> References: <1547061285-100329-1-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 default hierarchy doesn't support force_empty, but there are some usecases which create and remove memcgs very frequently, and the tasks in the memcg may just access the files which are unlikely accessed by anyone else. So, we prefer force_empty the memcg before rmdir'ing it to reclaim the page cache so that they don't get accumulated to incur unnecessary memory pressure. Since the memory pressure may incur direct reclaim to harm some latency sensitive applications. There is another patch which introduces asynchronous memory reclaim when offlining, but the behavior of force_empty is still needed by some usecases which want to get the memory reclaimed immediately. So, bring force_empty interface in default hierarchy too. Cc: Michal Hocko Cc: Johannes Weiner Cc: Shakeel Butt Signed-off-by: Yang Shi --- Documentation/admin-guide/cgroup-v2.rst | 14 ++++++++++++++ mm/memcontrol.c | 4 ++++ 2 files changed, 18 insertions(+) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 7bf3f12..0290c65 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1289,6 +1289,20 @@ PAGE_SIZE multiple when read back. Shows pressure stall information for memory. See Documentation/accounting/psi.txt for details. + memory.force_empty + This interface is provided to make cgroup's memory usage empty. + When writing anything to this + + # echo 0 > memory.force_empty + + the cgroup will be reclaimed and as many pages reclaimed as possible. + + The typical use case for this interface is before calling rmdir(). + Though rmdir() offlines memcg, but the memcg may still stay there due to + charged file caches. Some out-of-use page caches may keep charged until + memory pressure happens. If you want to avoid that, force_empty will be + useful. + Usage Guidelines ~~~~~~~~~~~~~~~~ diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ff50810..5d42a19 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5743,6 +5743,10 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of, .seq_show = wipe_on_offline_show, .write_u64 = wipe_on_offline_write, }, + { + .name = "force_empty", + .write = mem_cgroup_force_empty_write, + }, { } /* terminate */ }; -- 1.8.3.1