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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 678B6C282C2 for ; Wed, 23 Jan 2019 10:28:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 40F3720861 for ; Wed, 23 Jan 2019 10:28:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727205AbfAWK2I (ORCPT ); Wed, 23 Jan 2019 05:28:08 -0500 Received: from relay.sw.ru ([185.231.240.75]:53280 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726207AbfAWK2I (ORCPT ); Wed, 23 Jan 2019 05:28:08 -0500 Received: from [172.16.25.169] by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1gmFlL-0006Uz-IP; Wed, 23 Jan 2019 13:28:03 +0300 Subject: Re: [RFC PATCH] mm: vmscan: do not iterate all mem cgroups for global direct reclaim To: Yang Shi , mhocko@suse.com, hannes@cmpxchg.org, akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1548187782-108454-1-git-send-email-yang.shi@linux.alibaba.com> From: Kirill Tkhai Message-ID: Date: Wed, 23 Jan 2019 13:28:03 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <1548187782-108454-1-git-send-email-yang.shi@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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: memcg = mem_cgroup_iter(root, find_child(root->last_reclaim_child), &reclaim); do { if ((!global_reclaim(sc) || !current_is_kswapd()) && sc->nr_reclaimed >= sc->nr_to_reclaim) { root->last_reclaim_child = memcg->id; mem_cgroup_iter_break(root, memcg); break; } Kirill > Cc: Johannes Weiner > Cc: Michal Hocko > Signed-off-by: Yang Shi > --- > mm/vmscan.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index a714c4f..ced5a16 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2764,16 +2764,15 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc) > sc->nr_reclaimed - reclaimed); > > /* > - * Direct reclaim and kswapd have to scan all memory > - * cgroups to fulfill the overall scan target for the > - * node. > + * Kswapd have to scan all memory cgroups to fulfill > + * the overall scan target for the node. > * > * Limit reclaim, on the other hand, only cares about > * nr_to_reclaim pages to be reclaimed and it will > * retry with decreasing priority if one round over the > * whole hierarchy is not sufficient. > */ > - if (!global_reclaim(sc) && > + if ((!global_reclaim(sc) || !current_is_kswapd()) && > sc->nr_reclaimed >= sc->nr_to_reclaim) { > mem_cgroup_iter_break(root, memcg); > break; >