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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY 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 D8C67C43387 for ; Thu, 3 Jan 2019 18:20:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AFF5A2073D for ; Thu, 3 Jan 2019 18:20:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731179AbfACSUa (ORCPT ); Thu, 3 Jan 2019 13:20:30 -0500 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:45304 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727932AbfACSUa (ORCPT ); Thu, 3 Jan 2019 13:20:30 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01424;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0THTEjxM_1546539563; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0THTEjxM_1546539563) by smtp.aliyun-inc.com(127.0.0.1); Fri, 04 Jan 2019 02:19:26 +0800 Subject: Re: [PATCH 2/3] mm: memcontrol: do not try to do swap when force empty To: Shakeel Butt Cc: Michal Hocko , Johannes Weiner , Andrew Morton , Linux MM , LKML References: <1546459533-36247-1-git-send-email-yang.shi@linux.alibaba.com> <1546459533-36247-3-git-send-email-yang.shi@linux.alibaba.com> <763b97f5-ea9c-e3e6-7fd9-0ab42cf09ca8@linux.alibaba.com> From: Yang Shi Message-ID: Date: Thu, 3 Jan 2019 10:19:23 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/3/19 9:03 AM, Shakeel Butt wrote: > On Thu, Jan 3, 2019 at 8:57 AM Yang Shi wrote: >> >> >> On 1/2/19 1:45 PM, Shakeel Butt wrote: >>> On Wed, Jan 2, 2019 at 12:06 PM Yang Shi wrote: >>>> The typical usecase of force empty is to try to reclaim as much as >>>> possible memory before offlining a memcg. Since there should be no >>>> attached tasks to offlining memcg, the tasks anonymous pages would have >>>> already been freed or uncharged. >>> Anon pages can come from tmpfs files as well. >> Yes, but they are charged to swap space as regular anon pages. >> > The point was the lifetime of tmpfs anon pages are not tied to any > task. Even though there aren't any task attached to a memcg, the tmpfs > anon pages will remain charged. Other than that, the old anon pages of > a task which have migrated away might still be charged to the old > memcg (if move_charge_at_immigrate is not set). Yes, my understanding is even though they are swapped out but they are still charged to memsw for cgroupv1. force_empty is supposed to reclaim as much as possible memory, here I'm supposed "reclaim" also means "uncharge". Even though the anon pages are still charged to the old memcg, it will be moved the new memcg when the old one is deleted, or the pages will be just released if the task is killed. So, IMHO, I don't see the point why swapping anon pages when doing force_empty. Thanks, Yang >>>> Even though anonymous pages get >>>> swapped out, but they still get charged to swap space. So, it sounds >>>> pointless to do swap for force empty. >>>> >>> I understand that force_empty is typically used before rmdir'ing a >>> memcg but it might be used differently by some users. We use this >>> interface to test memory reclaim behavior (anon and file). >> Thanks for sharing your usecase. So, you uses this for test only? >> > Yes. > > Shakeel