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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 37443C433DF for ; Fri, 29 May 2020 05:37:21 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id F0284207D3 for ; Fri, 29 May 2020 05:37:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F0284207D3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 92B518001A; Fri, 29 May 2020 01:37:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8B59280010; Fri, 29 May 2020 01:37:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 77CE18001A; Fri, 29 May 2020 01:37:20 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0020.hostedemail.com [216.40.44.20]) by kanga.kvack.org (Postfix) with ESMTP id 5BECB80010 for ; Fri, 29 May 2020 01:37:20 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 1B29A181AEF1A for ; Fri, 29 May 2020 05:37:20 +0000 (UTC) X-FDA: 76868648640.08.sense55_5ce7807393d46 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id 0480B1819E798 for ; Fri, 29 May 2020 05:37:19 +0000 (UTC) X-HE-Tag: sense55_5ce7807393d46 X-Filterd-Recvd-Size: 3066 Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by imf38.hostedemail.com (Postfix) with ESMTP for ; Fri, 29 May 2020 05:37:18 +0000 (UTC) IronPort-SDR: hsVyE8jS7U84HOVGhWhWZLLhuHO57qW1adKYGGUeG6sreevnfgkaijapJ7faUZgLWlHrVRBiL7 KOfEXFxIm0vQ== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 May 2020 22:37:16 -0700 IronPort-SDR: 6ypjrCpGe+u2ZKOsSiOCn+oHK1f4MCoA7qld/0DTbkf5PThk4gEcABNY/WvkBHNGUS/PuTL+S/ vO8+CcBfH0Vw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,447,1583222400"; d="scan'208";a="302724034" Received: from shbuild999.sh.intel.com (HELO localhost) ([10.239.146.107]) by fmsmga002.fm.intel.com with ESMTP; 28 May 2020 22:37:13 -0700 Date: Fri, 29 May 2020 13:37:13 +0800 From: Feng Tang To: Qian Cai Cc: Andrew Morton , Michal Hocko , Johannes Weiner , Matthew Wilcox , Mel Gorman , Kees Cook , andi.kleen@intel.com, tim.c.chen@intel.com, dave.hansen@intel.com, ying.huang@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Konstantin Khlebnikov Subject: Re: [PATCH v4 3/4] mm/util.c: remove the VM_WARN_ONCE for vm_committed_as underflow check Message-ID: <20200529053713.GH93879@shbuild999.sh.intel.com> References: <1590714370-67182-1-git-send-email-feng.tang@intel.com> <1590714370-67182-4-git-send-email-feng.tang@intel.com> <20200529024928.GA4566@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200529024928.GA4566@lca.pw> User-Agent: Mutt/1.5.24 (2015-08-30) X-Rspamd-Queue-Id: 0480B1819E798 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, May 28, 2020 at 10:49:28PM -0400, Qian Cai wrote: > On Fri, May 29, 2020 at 09:06:09AM +0800, Feng Tang wrote: > > As is explained by Michal Hocko: > > > > : Looking at the history, this has been added by 82f71ae4a2b8 > > : ("mm: catch memory commitment underflow") to have a safety check > > : for issues which have been fixed. There doesn't seem to be any bug > > : reports mentioning this splat since then so it is likely just > > : spending cycles for a hot path (yes many people run with DEBUG_VM) > > : without a strong reason. > > Hmm, it looks like the warning is still useful to catch issues in, > > https://lore.kernel.org/linux-mm/20140624201606.18273.44270.stgit@zurg > https://lore.kernel.org/linux-mm/54BB9A32.7080703@oracle.com/ > > After read the whole discussion in that thread, I actually disagree with > Michal. In order to get ride of this existing warning, it is rather > someone needs a strong reason that could prove the performance hit is > noticeable with some data. One problem with current check is percpu_counter_read(&vm_committed_as) is not accurate, and percpu_counter_sum() is way too heavy. Thanks, Feng