From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id E27B38E001A for ; Wed, 23 Jan 2019 07:11:02 -0500 (EST) Received: by mail-ed1-f70.google.com with SMTP id e29so869057ede.19 for ; Wed, 23 Jan 2019 04:11:02 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id b24si1784756eju.264.2019.01.23.04.11.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 23 Jan 2019 04:11:01 -0800 (PST) Date: Wed, 23 Jan 2019 13:10:58 +0100 From: Michal Hocko Subject: Re: [RFC PATCH] mm: vmscan: do not iterate all mem cgroups for global direct reclaim Message-ID: <20190123121058.GW4087@dhcp22.suse.cz> References: <1548187782-108454-1-git-send-email-yang.shi@linux.alibaba.com> <20190123110254.GU4087@dhcp22.suse.cz> <9bd4044b-63d0-b24f-a108-3061c00ed131@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9bd4044b-63d0-b24f-a108-3061c00ed131@virtuozzo.com> Sender: owner-linux-mm@kvack.org List-ID: To: Kirill Tkhai Cc: Yang Shi , hannes@cmpxchg.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Wed 23-01-19 14:05:28, Kirill Tkhai wrote: > On 23.01.2019 14:02, Michal Hocko wrote: > > On Wed 23-01-19 13:28:03, Kirill Tkhai wrote: > >> On 22.01.2019 23:09, Yang Shi wrote: > >>> In current implementation, both kswapd and direct reclaim has to iterate > >>> all mem cgroups. It is not a problem before offline mem cgroups could > >>> be iterated. But, currently with iterating offline mem cgroups, it > >>> could be very time consuming. In our workloads, we saw over 400K mem > >>> cgroups accumulated in some cases, only a few hundred are online memcgs. > >>> Although kswapd could help out to reduce the number of memcgs, direct > >>> reclaim still get hit with iterating a number of offline memcgs in some > >>> cases. We experienced the responsiveness problems due to this > >>> occassionally. > >>> > >>> Here just break the iteration once it reclaims enough pages as what > >>> memcg direct reclaim does. This may hurt the fairness among memcgs > >>> since direct reclaim may awlays do reclaim from same memcgs. But, it > >>> sounds ok since direct reclaim just tries to reclaim SWAP_CLUSTER_MAX > >>> pages and memcgs can be protected by min/low. > >> > >> In case of we stop after SWAP_CLUSTER_MAX pages are reclaimed; it's possible > >> the following situation. Memcgs, which are closest to root_mem_cgroup, will > >> become empty, and you will have to iterate over empty memcg hierarchy long time, > >> just to find a not empty memcg. > >> > >> I'd suggest, we should not lose fairness. We may introduce > >> mem_cgroup::last_reclaim_child parameter to save a child > >> (or its id), where the last reclaim was interrupted. Then > >> next reclaim should start from this child: > > > > Why is not our reclaim_cookie based caching sufficient? > > Hm, maybe I missed them. Do cookies already implement this functionality? Have a look at mem_cgroup_iter -- Michal Hocko SUSE Labs