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 DC0BCC56201 for ; Tue, 24 Nov 2020 13:39:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8A58620782 for ; Tue, 24 Nov 2020 13:39:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388448AbgKXNjo (ORCPT ); Tue, 24 Nov 2020 08:39:44 -0500 Received: from mx2.suse.de ([195.135.220.15]:39120 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387693AbgKXNjo (ORCPT ); Tue, 24 Nov 2020 08:39:44 -0500 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: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/23/20 4:10 PM, Charan Teja Kalla wrote: > > 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 buffer >>> 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. >> >> 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. > > 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 one > 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 flooded when only the rest of __dump_page() is printed? (which is also 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 prevent flooding we generally have ratelimiting, how about that? Also agreed with Michal that page_owner is explicitly enabled debugging option and if you use it in production, that's rather surprising to me, and possibly more rare than DEBUG_VM, which IIRC Fedora kernels use.