From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf1-f71.google.com (mail-lf1-f71.google.com [209.85.167.71]) by kanga.kvack.org (Postfix) with ESMTP id 86EB48E001A for ; Wed, 23 Jan 2019 06:05:32 -0500 (EST) Received: by mail-lf1-f71.google.com with SMTP id g16so122403lfb.22 for ; Wed, 23 Jan 2019 03:05:32 -0800 (PST) Received: from relay.sw.ru (relay.sw.ru. [185.231.240.75]) by mx.google.com with ESMTPS id j24si2621374lfh.19.2019.01.23.03.05.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 23 Jan 2019 03:05:30 -0800 (PST) Subject: Re: [RFC PATCH] mm: vmscan: do not iterate all mem cgroups for global direct reclaim References: <1548187782-108454-1-git-send-email-yang.shi@linux.alibaba.com> <20190123110254.GU4087@dhcp22.suse.cz> From: Kirill Tkhai Message-ID: <9bd4044b-63d0-b24f-a108-3061c00ed131@virtuozzo.com> Date: Wed, 23 Jan 2019 14:05:28 +0300 MIME-Version: 1.0 In-Reply-To: <20190123110254.GU4087@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Yang Shi , hannes@cmpxchg.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org 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? Kirill