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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1058CC433F5 for ; Fri, 8 Oct 2021 09:16:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E9B3D60F6C for ; Fri, 8 Oct 2021 09:16:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236858AbhJHJSc (ORCPT ); Fri, 8 Oct 2021 05:18:32 -0400 Received: from out30-54.freemail.mail.aliyun.com ([115.124.30.54]:44325 "EHLO out30-54.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236335AbhJHJS1 (ORCPT ); Fri, 8 Oct 2021 05:18:27 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R211e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04407;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0Ur-5elq_1633684590; Received: from 30.21.164.80(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0Ur-5elq_1633684590) by smtp.aliyun-inc.com(127.0.0.1); Fri, 08 Oct 2021 17:16:30 +0800 Subject: Re: [PATCH 0/2] Support hugetlb charge moving at task migration To: Michal Hocko Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: From: Baolin Wang Message-ID: Date: Fri, 8 Oct 2021 17:17:12 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/10/8 15:12, Michal Hocko wrote: > On Thu 07-10-21 23:39:15, Baolin Wang wrote: >> Hi Michal, >> >> (Sorry for late reply due to my holidays) >> On 2021/9/30 18:46, Michal Hocko wrote: >>> On Wed 29-09-21 18:19:26, Baolin Wang wrote: >>>> Hi, >>>> >>>> Now in the hugetlb cgroup, charges associated with a task aren't moved >>>> to the new hugetlb cgroup at task migration, which is odd for hugetlb >>>> cgroup usage. >>> >>> Could you elaborate some more about the usecase and/or problems you see >>> with the existing semantic? >> >> The problems is that, it did not check if the tasks can move to the new >> hugetlb cgroup if the new hugetlb cgroup has a limitation, and the hugetlb >> cgroup usage is incorrect when moving tasks among hugetlb cgroups. > > Could you be more specific please? What do you mean by cgroup usage is > incorrect? Ideally could you describe your usecase? Sorry for confusing, what I mean is, when tasks from one hugetlb cgroup are migrated to a new hugetlb cgroup, the new hugetlb cgroup's hugetlb page usage is not increased accordingly. The issue I found is just from my testing for the hugetlb cgroup, and I think this is not resonable if we've already set a hugetlb limitation for a cgroup, but we always ignore it when tasks migration among hugetlb cgroups. >>>> This patch set adds hugetlb cgroup charge moving when >>>> migrate tasks among cgroups, which are based on the memcg charge moving. >>> >>> Memcg charge moving has shown some problems over time and hence this is >>> not part of cgroup v2 interface anymore. Even for cgroup v1 this has >> >> Sorry, I missed this part, could you elaborate on the issues? I can have a >> close look about the problems of memcg charge moving. > > The operation is quite expensive. Synchronization with charging is not > trivial. I do not have the full list handy but you can search the > mm mailing list archives for more information. Sure, thanks. > >>> been an opt-in. I do not see anything like that in this patch series. >>> Why should all existing workloads follow a different semantic during >>> task migration now? >> >> But I think it is reasonable for some cases moving the old charging to the >> new cgroup when task migration. Maybe I can add a new hugetlb cgroup file to >> control if need this or not? > > It would be good to describe those use cases and why they really need > this. Because as things stand now, the charge migration is not supported > in cgroup v2 for memory cgroup controller and there are no plans to add > the support so it would be quite unexpected that hugetlb controller > would behave differently. And cgroup v1 is considered legacy and new > features are ususally not added as there is a hope to move users to v2. OK, understood. Seems you have a strong opinion that it is unnecessary to introduce this feature for cgroup v1 now, then I will drop this patch set. Thanks for your input.