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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 D550EC63798 for ; Tue, 24 Nov 2020 13:39:46 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5C56320782 for ; Tue, 24 Nov 2020 13:39:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5C56320782 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B5F796B0138; Tue, 24 Nov 2020 08:39:45 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B0DFB6B013A; Tue, 24 Nov 2020 08:39:45 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A4CA96B013B; Tue, 24 Nov 2020 08:39:45 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0250.hostedemail.com [216.40.44.250]) by kanga.kvack.org (Postfix) with ESMTP id 8E5B06B0138 for ; Tue, 24 Nov 2020 08:39:45 -0500 (EST) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 589ED1EE6 for ; Tue, 24 Nov 2020 13:39:45 +0000 (UTC) X-FDA: 77519419530.15.trade66_3b063352736e Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id 320491814B0C1 for ; Tue, 24 Nov 2020 13:39:45 +0000 (UTC) X-HE-Tag: trade66_3b063352736e X-Filterd-Recvd-Size: 3076 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf33.hostedemail.com (Postfix) with ESMTP for ; Tue, 24 Nov 2020 13:39:44 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 58507AD1E; Tue, 24 Nov 2020 13:39:43 +0000 (UTC) To: Charan Teja Kalla , Michal Hocko Cc: akpm@linux-foundation.org, david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "vinmenon@codeaurora.org" References: <1606140196-6053-1-git-send-email-charante@codeaurora.org> <20201123141354.GQ27488@dhcp22.suse.cz> From: Vlastimil Babka Subject: Re: [PATCH] mm: memory_hotplug: put migration failure information under DEBUG_VM Message-ID: <775a56a9-b301-31bb-cd6d-8b82b1dd4d65@suse.cz> Date: Tue, 24 Nov 2020 14:39:42 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.3 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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 11/23/20 4:10 PM, Charan Teja Kalla wrote: >=20 > Thanks Michal! > On 11/23/2020 7:43 PM, Michal Hocko wrote: >> On Mon 23-11-20 19:33:16, Charan Teja Reddy wrote: >>> When the pages are failed to get isolate or migrate, the page owner >>> information along with page info is dumped. If there are continuous >>> failures in migration(say page is pinned) or isolation, the log buffe= r >>> is simply getting flooded with the page owner information. As most of >>> the times page info is sufficient to know the causes for failures of >>> migration or isolation, place the page owner information under DEBUG_= VM. >>=20 >> I do not see why this path is any different from others that call >> dump_page. Page owner can add a very valuable information to debug >> the underlying reasons for failures here. It is an opt-in debugging >> feature which needs to be enabled explicitly. So I would argue users >> are ready to accept a lot of data in the kernel log. >=20 > Just thinking how frequently failures can happen in those paths. In the > memory hotplug path, we can flood the page owner logs just by making on= e > page pinned. Say If it is anonymous page, the page owner information So you say it's flooded when page_owner info is included, but not=20 flooded when only the rest of __dump_page() is printed? (which is also=20 not just one or two lines). That has to be very specific rate of failures= . Anyway I don't like the solution with arbitrary config option. To=20 prevent flooding we generally have ratelimiting, how about that? Also agreed with Michal that page_owner is explicitly enabled debugging=20 option and if you use it in production, that's rather surprising to me,=20 and possibly more rare than DEBUG_VM, which IIRC Fedora kernels use.