From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH] mm/memcontrol: Add the drop_cache interface for cgroup v2 Date: Mon, 21 Sep 2020 10:12:00 +0200 Message-ID: <20200921081200.GE12990@dhcp22.suse.cz> References: <20200921080255.15505-1-zangchunxin@bytedance.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1600675922; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qY5z/CIzbaqHx8s2HYRdo5vtY/9cgm6CVe0rMQIWXjg=; b=NlpFxE4kmST4SqiC5KofXcdP2j2eEf3octfP5pb/ZkthT+R+VMr0ShAlQF0vVtz0GEe+GO D26n3IIIRUqhBlVspyCQkqlGByh3LG83HorXcqlE6pFmkl+VuZQXmVa7ttvda40L06GP2m RMCAgOXkCA9XWEXTU8TB5d2ETbPr2Qk= Content-Disposition: inline In-Reply-To: <20200921080255.15505-1-zangchunxin@bytedance.com> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: zangchunxin@bytedance.com Cc: hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, tj@kernel.org, lizefan@huawei.com, corbet@lwn.net, ast@kernel.org, daniel@iogearbox.net, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, andriin@fb.com, john.fastabend@gmail.com, kpsingh@chromium.org, cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org On Mon 21-09-20 16:02:55, zangchunxin@bytedance.com wrote: > From: Chunxin Zang > > In the cgroup v1, we have 'force_mepty' interface. This is very > useful for userspace to actively release memory. But the cgroup > v2 does not. > > This patch reuse cgroup v1's function, but have a new name for > the interface. Because I think 'drop_cache' may be is easier to > understand :) This should really explain a usecase. Global drop_caches is a terrible interface and it has caused many problems in the past. People have learned to use it as a remedy to any problem they might see and cause other problems without realizing that. This is the reason why we even log each attempt to drop caches. I would rather not repeat the same mistake on the memcg level unless there is a very strong reason for it. > Signed-off-by: Chunxin Zang > --- > Documentation/admin-guide/cgroup-v2.rst | 11 +++++++++++ > mm/memcontrol.c | 5 +++++ > 2 files changed, 16 insertions(+) > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > index ce3e05e41724..fbff959c8116 100644 > --- a/Documentation/admin-guide/cgroup-v2.rst > +++ b/Documentation/admin-guide/cgroup-v2.rst > @@ -1181,6 +1181,17 @@ PAGE_SIZE multiple when read back. > high limit is used and monitored properly, this limit's > utility is limited to providing the final safety net. > > + memory.drop_cache > + A write-only single value file which exists on non-root > + cgroups. > + > + Provide a mechanism for users to actively trigger memory > + reclaim. The cgroup will be reclaimed and as many pages > + reclaimed as possible. > + > + It will broke low boundary. Because it tries to reclaim the > + memory many times, until the memory drops to a certain level. > + > memory.oom.group > A read-write single value file which exists on non-root > cgroups. The default value is "0". > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 0b38b6ad547d..98646484efff 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -6226,6 +6226,11 @@ static struct cftype memory_files[] = { > .write = memory_max_write, > }, > { > + .name = "drop_cache", > + .flags = CFTYPE_NOT_ON_ROOT, > + .write = mem_cgroup_force_empty_write, > + }, > + { > .name = "events", > .flags = CFTYPE_NOT_ON_ROOT, > .file_offset = offsetof(struct mem_cgroup, events_file), > -- > 2.11.0 -- Michal Hocko SUSE Labs