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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 18007C04EB9 for ; Mon, 3 Dec 2018 17:22:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DE4C9208A3 for ; Mon, 3 Dec 2018 17:22:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DE4C9208A3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726785AbeLCRWK (ORCPT ); Mon, 3 Dec 2018 12:22:10 -0500 Received: from mx2.suse.de ([195.135.220.15]:34238 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726512AbeLCRWJ (ORCPT ); Mon, 3 Dec 2018 12:22:09 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 72B41AED5; Mon, 3 Dec 2018 17:22:04 +0000 (UTC) Date: Mon, 3 Dec 2018 18:22:02 +0100 From: Michal Hocko To: Xunlei Pang Cc: Roman Gushchin , Johannes Weiner , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 2/3] mm/vmscan: Enable kswapd to reclaim low-protected memory Message-ID: <20181203172007.GG31738@dhcp22.suse.cz> References: <20181203080119.18989-1-xlpang@linux.alibaba.com> <20181203080119.18989-2-xlpang@linux.alibaba.com> <20181203115646.GP31738@dhcp22.suse.cz> <54a3f0a6-6e7d-c620-97f2-ac567c057bc2@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <54a3f0a6-6e7d-c620-97f2-ac567c057bc2@linux.alibaba.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 03-12-18 23:20:31, Xunlei Pang wrote: > On 2018/12/3 下午7:56, Michal Hocko wrote: > > On Mon 03-12-18 16:01:18, Xunlei Pang wrote: > >> There may be cgroup memory overcommitment, it will become > >> even common in the future. > >> > >> Let's enable kswapd to reclaim low-protected memory in case > >> of memory pressure, to mitigate the global direct reclaim > >> pressures which could cause jitters to the response time of > >> lantency-sensitive groups. > > > > Please be more descriptive about the problem you are trying to handle > > here. I haven't actually read the patch but let me emphasise that the > > low limit protection is important isolation tool. And allowing kswapd to > > reclaim protected memcgs is going to break the semantic as it has been > > introduced and designed. > > We have two types of memcgs: online groups(important business) > and offline groups(unimportant business). Online groups are > all configured with MAX low protection, while offline groups > are not at all protected(with default 0 low). > > When offline groups are overcommitted, the global memory pressure > suffers. This will cause the memory allocations from online groups > constantly go to the slow global direct reclaim in order to reclaim > online's page caches, as kswap is not able to reclaim low-protection > memory. low is not hard limit, it's reasonable to be reclaimed by > kswapd if there's no other reclaimable memory. I am sorry I still do not follow. What role do offline cgroups play. Those are certainly not low mem protected because mem_cgroup_css_offline will reset them to 0. -- Michal Hocko SUSE Labs