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 E70A68E00F9 for ; Fri, 4 Jan 2019 19:21:10 -0500 (EST) Received: by mail-pl1-f197.google.com with SMTP id ay11so28095314plb.20 for ; Fri, 04 Jan 2019 16:21:10 -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 j132si4261668pfc.84.2019.01.04.16.21.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 04 Jan 2019 16:21:09 -0800 (PST) From: Yang Shi Subject: [v2 PATCH 4/5] mm: memcontrol: bring force_empty into default hierarchy Date: Sat, 5 Jan 2019 08:19:19 +0800 Message-Id: <1546647560-40026-5-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 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 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 5a13c6b..c4a7dc7 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