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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 828E7C433DB for ; Wed, 10 Feb 2021 09:51:10 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id DF75364E40 for ; Wed, 10 Feb 2021 09:51:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DF75364E40 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 497F66B0006; Wed, 10 Feb 2021 04:51:09 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 447F96B006C; Wed, 10 Feb 2021 04:51:09 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 30F046B006E; Wed, 10 Feb 2021 04:51:09 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0029.hostedemail.com [216.40.44.29]) by kanga.kvack.org (Postfix) with ESMTP id 17AF46B0006 for ; Wed, 10 Feb 2021 04:51:09 -0500 (EST) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id DB5DF824805A for ; Wed, 10 Feb 2021 09:51:08 +0000 (UTC) X-FDA: 77801889816.21.shoes54_2917ff52760f Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id BC7F218559306 for ; Wed, 10 Feb 2021 09:51:08 +0000 (UTC) X-HE-Tag: shoes54_2917ff52760f X-Filterd-Recvd-Size: 4348 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf25.hostedemail.com (Postfix) with ESMTP for ; Wed, 10 Feb 2021 09:51:08 +0000 (UTC) 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=1612950667; h=from:from:reply-to: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=CAFzAyZy/KFZTsu+ARXaCj+Xnf0VYpa/fyIfFuwi9+E=; b=YUq56y6mtYH/Zv/QM5JMteooatovb8ZVwTA95QkzipN8TrrweOCA2kd/E4vxFBA8rRv/TC KacdaHK0HaJxMz0S1v9EbDcIGgfr77mN3pQpz3D4aIvttYIWmFZX86ZrhHqQzGuaRftQz/ +rE8Is9r5TMyPepqPzAgq8PzSP3lPw0= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 9C0F3AF7F; Wed, 10 Feb 2021 09:51:06 +0000 (UTC) Date: Wed, 10 Feb 2021 10:51:04 +0100 From: Michal Hocko To: Tim Chen Cc: Andrew Morton , Johannes Weiner , Vladimir Davydov , Dave Hansen , Ying Huang , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] mm: Force update of mem cgroup soft limit tree on usage excess Message-ID: References: <90ef1dbc8ba6112794a3d09ecfed73f385f08eb7.1612902157.git.tim.c.chen@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <90ef1dbc8ba6112794a3d09ecfed73f385f08eb7.1612902157.git.tim.c.chen@linux.intel.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue 09-02-21 12:29:46, Tim Chen wrote: > To rate limit updates to the mem cgroup soft limit tree, we only perform > updates every SOFTLIMIT_EVENTS_TARGET (defined as 1024) memory events. > > However, this sampling based updates may miss a critical update: i.e. when > the mem cgroup first exceeded its limit but it was not on the soft limit tree. > It should be on the tree at that point so it could be subjected to soft > limit page reclaim. If the mem cgroup had few memory events compared with > other mem cgroups, we may not update it and place in on the mem cgroup > soft limit tree for many memory events. And this mem cgroup excess > usage could creep up and the mem cgroup could be hidden from the soft > limit page reclaim for a long time. Have you observed this happening in the real life? I do agree that the threshold based updates of the tree is not ideal but the whole soft reclaim code is far from optimal. So why do we care only now? The feature is essentially dead and fine tuning it sounds like a step back to me. > Fix this issue by forcing an update to the mem cgroup soft limit tree if a > mem cgroup has exceeded its memory soft limit but it is not on the mem > cgroup soft limit tree. > > Reviewed-by: Ying Huang > Signed-off-by: Tim Chen > --- > mm/memcontrol.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index a51bf90732cb..d72449eeb85a 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -985,15 +985,22 @@ static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg, > */ > static void memcg_check_events(struct mem_cgroup *memcg, struct page *page) > { > + struct mem_cgroup_per_node *mz; > + bool force_update = false; > + > + mz = mem_cgroup_nodeinfo(memcg, page_to_nid(page)); > + if (mz && !mz->on_tree && soft_limit_excess(mz->memcg) > 0) > + force_update = true; > + > /* threshold event is triggered in finer grain than soft limit */ > - if (unlikely(mem_cgroup_event_ratelimit(memcg, > + if (unlikely((force_update) || mem_cgroup_event_ratelimit(memcg, > MEM_CGROUP_TARGET_THRESH))) { > bool do_softlimit; > > do_softlimit = mem_cgroup_event_ratelimit(memcg, > MEM_CGROUP_TARGET_SOFTLIMIT); > mem_cgroup_threshold(memcg); > - if (unlikely(do_softlimit)) > + if (unlikely((force_update) || do_softlimit)) > mem_cgroup_update_tree(memcg, page); > } > } > -- > 2.20.1 -- Michal Hocko SUSE Labs