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 B29E1CA9EB9 for ; Thu, 24 Oct 2019 03:33:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8D1782173B for ; Thu, 24 Oct 2019 03:33:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437289AbfJXDdR (ORCPT ); Wed, 23 Oct 2019 23:33:17 -0400 Received: from mga12.intel.com ([192.55.52.136]:31425 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392870AbfJXDdR (ORCPT ); Wed, 23 Oct 2019 23:33:17 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 23 Oct 2019 20:33:16 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.68,223,1569308400"; d="scan'208";a="188457716" Received: from shbuild999.sh.intel.com (HELO localhost) ([10.239.147.113]) by orsmga007.jf.intel.com with ESMTP; 23 Oct 2019 20:33:13 -0700 Date: Thu, 24 Oct 2019 11:33:13 +0800 From: Feng Tang To: Waiman Long Cc: Qian Cai , Andrew Morton , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Johannes Weiner , Michal Hocko , Roman Gushchin , Vlastimil Babka , Konstantin Khlebnikov , Jann Horn , Song Liu , Greg Kroah-Hartman , Rafael Aquini Subject: Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo Message-ID: <20191024033313.GA42124@shbuild999.sh.intel.com> References: <20191022162156.17316-1-longman@redhat.com> <20191022145902.d9c4a719c0b32175e06e4eee@linux-foundation.org> <2236495a-ead0-e08e-3fb6-f3ab906b75b6@redhat.com> <1571842093.5937.84.camel@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 23, 2019 at 11:01:04PM +0800, Waiman Long wrote: > On 10/23/19 10:48 AM, Qian Cai wrote: > >>> this still isn't a bulletproof fix. Maybe just terminate the list > >>> walk if freecount reaches 1024. Would anyone really care? > >>> > >>> Sigh. I wonder if anyone really uses this thing for anything > >>> important. Can we just remove it all? > >>> > >> Removing it will be a breakage of kernel API. > > Who cares about breaking this part of the API that essentially nobody will use > > this file? > > > There are certainly tools that use /proc/pagetypeinfo and this is how > the problem is found. I am not against removing it, but we have to be > careful and deprecate it in way that minimize user impact. We have been using the /proc/pagetypeinfo for debugging, mainly for client platforms like phones/tablets. We met problems like very slow system response or OOM things, and many of them could be related with memory pressure or fragmentation issues, where monitoring /proc/pagetypeinfo will be very useful for debugging. So I think Michal's idea to change it to 0400 is a good idea. Thanks, Feng > Cheers, > Longman > >