From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 324DAC43464 for ; Mon, 21 Sep 2020 08:12:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E62B6216C4 for ; Mon, 21 Sep 2020 08:12:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="NlpFxE4k" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726556AbgIUIME (ORCPT ); Mon, 21 Sep 2020 04:12:04 -0400 Received: from mx2.suse.de ([195.135.220.15]:42198 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726475AbgIUIME (ORCPT ); Mon, 21 Sep 2020 04:12:04 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de 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= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7B8B2B270; Mon, 21 Sep 2020 08:12:38 +0000 (UTC) Date: Mon, 21 Sep 2020 10:12:00 +0200 From: Michal Hocko 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 Subject: Re: [PATCH] mm/memcontrol: Add the drop_cache interface for cgroup v2 Message-ID: <20200921081200.GE12990@dhcp22.suse.cz> References: <20200921080255.15505-1-zangchunxin@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200921080255.15505-1-zangchunxin@bytedance.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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