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 84360ECDFB3 for ; Mon, 16 Jul 2018 11:08:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3AF86208C3 for ; Mon, 16 Jul 2018 11:08:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3AF86208C3 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 S1729228AbeGPLfl (ORCPT ); Mon, 16 Jul 2018 07:35:41 -0400 Received: from mx2.suse.de ([195.135.220.15]:49506 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727953AbeGPLfl (ORCPT ); Mon, 16 Jul 2018 07:35:41 -0400 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 E80FFADC2; Mon, 16 Jul 2018 11:08:45 +0000 (UTC) Date: Mon, 16 Jul 2018 13:08:45 +0200 From: Michal Hocko To: Yafang Shao Cc: Johannes Weiner , Vladimir Davydov , Cgroups , Linux MM , LKML Subject: Re: [PATCH] mm: avoid bothering interrupted task when charge memcg in softirq Message-ID: <20180716110845.GK17280@dhcp22.suse.cz> References: <1531557122-12540-1-git-send-email-laoar.shao@gmail.com> <20180716075836.GC17280@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 16-07-18 17:45:06, Yafang Shao wrote: > On Mon, Jul 16, 2018 at 3:58 PM, Michal Hocko wrote: > > On Sat 14-07-18 16:32:02, Yafang Shao wrote: > >> try_charge maybe executed in packet receive path, which is in interrupt > >> context. > >> In this situation, the 'current' is the interrupted task, which may has > >> no relation to the rx softirq, So it is nonsense to use 'current'. > >> > >> Avoid bothering the interrupted if page_counter_try_charge failes. > > > > I agree with Shakeel that this changelog asks for more information about > > "why it matters". Small inconsistencies should be tolerable because the > > state we rely on is so rarely set that it shouldn't make a visible > > difference in practice. > > > > HI Michal, > > No, it can make a visible difference in pratice. > The difference is in __sk_mem_raise_allocated(). > > Without this patch, if the random interrupted task is oom victim or > fatal signal pending or exiting, the charge will success anyway. That > means the cgroup limit doesn't work in this situation. > > With this patch, in the same situation the charged memory will be > uncharged as it hits the memcg limit. > > That is okay if the memcg of the interrupted task is same with the > sk->sk_memcg, but it may not okay if they are difference. > > I'm trying to prove it, but seems it's very hard to produce this issue. So it is possible that this is so marginal that it doesn't make any _practical_ impact after all. -- Michal Hocko SUSE Labs