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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 E9A35C43142 for ; Mon, 25 Jun 2018 14:02:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ABB5225AE5 for ; Mon, 25 Jun 2018 14:02:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org ABB5225AE5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=sony.com 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 S934164AbeFYOCX convert rfc822-to-8bit (ORCPT ); Mon, 25 Jun 2018 10:02:23 -0400 Received: from seldsegrel01.sonyericsson.com ([37.139.156.29]:17668 "EHLO SELDSEGREL01.sonyericsson.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755531AbeFYOCW (ORCPT ); Mon, 25 Jun 2018 10:02:22 -0400 Subject: Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer. To: Michal Hocko CC: Tetsuo Handa , , , , References: <1529493638-6389-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20180620115531.GL13685@dhcp22.suse.cz> <3d27f26e-68ba-d3c0-9518-cebeb2689aec@sony.com> <20180625130756.GK28965@dhcp22.suse.cz> From: peter enderborg Message-ID: <4c6f9bd5-e959-c0bd-53db-988e07644754@sony.com> Date: Mon, 25 Jun 2018 16:02:20 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180625130756.GK28965@dhcp22.suse.cz> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8BIT Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/25/2018 03:07 PM, Michal Hocko wrote: > On Mon 25-06-18 15:03:40, peter enderborg wrote: >> On 06/20/2018 01:55 PM, Michal Hocko wrote: >>> On Wed 20-06-18 20:20:38, Tetsuo Handa wrote: >>>> Sleeping with oom_lock held can cause AB-BA lockup bug because >>>> __alloc_pages_may_oom() does not wait for oom_lock. Since >>>> blocking_notifier_call_chain() in out_of_memory() might sleep, sleeping >>>> with oom_lock held is currently an unavoidable problem. >>> Could you be more specific about the potential deadlock? Sleeping while >>> holding oom lock is certainly not nice but I do not see how that would >>> result in a deadlock assuming that the sleeping context doesn't sleep on >>> the memory allocation obviously. >> It is a mutex you are supposed to be able to sleep.  It's even exported. > What do you mean? oom_lock is certainly not exported for general use. It > is not local to oom_killer.c just because it is needed in other _mm_ > code. > It  is in the oom.h file include/linux/oom.h, if it that sensitive it should be in mm/ and a documented note about the special rules. It is only used in drivers/tty/sysrq.c and that be replaced by a help function in mm that do the  oom stuff. >>>> As a preparation for not to sleep with oom_lock held, this patch brings >>>> OOM notifier callbacks to outside of OOM killer, with two small behavior >>>> changes explained below. >>> Can we just eliminate this ugliness and remove it altogether? We do not >>> have that many notifiers. Is there anything fundamental that would >>> prevent us from moving them to shrinkers instead? >> >> @Hocko Do you remember the lowmemorykiller from android? Some things >> might not be the right thing for shrinkers. > Just that lmk did it wrong doesn't mean others have to follow. > If all you have is a hammer, everything looks like a nail. (I don’t argument that it was right) But if you don’t have a way to interact with the memory system we will get attempts like lmk.  Oom notifiers and vmpressure is for this task better than shrinkers.