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=-5.2 required=3.0 tests=BAYES_00, 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 17FDFC4363D for ; Fri, 2 Oct 2020 10:19:58 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 62634206FA for ; Fri, 2 Oct 2020 10:19:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 62634206FA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=techsingularity.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 8EE7B6B0068; Fri, 2 Oct 2020 06:19:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 89EB6900002; Fri, 2 Oct 2020 06:19:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7B64F6B006E; Fri, 2 Oct 2020 06:19:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0145.hostedemail.com [216.40.44.145]) by kanga.kvack.org (Postfix) with ESMTP id 4C95F6B0068 for ; Fri, 2 Oct 2020 06:19:56 -0400 (EDT) Received: from smtpin22.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id D5DB48249980 for ; Fri, 2 Oct 2020 10:19:55 +0000 (UTC) X-FDA: 77326589550.22.fifth05_3606fc1271a3 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin22.hostedemail.com (Postfix) with ESMTP id AC6CC18038E60 for ; Fri, 2 Oct 2020 10:19:55 +0000 (UTC) X-HE-Tag: fifth05_3606fc1271a3 X-Filterd-Recvd-Size: 3207 Received: from outbound-smtp18.blacknight.com (outbound-smtp18.blacknight.com [46.22.139.245]) by imf28.hostedemail.com (Postfix) with ESMTP for ; Fri, 2 Oct 2020 10:19:54 +0000 (UTC) Received: from mail.blacknight.com (pemlinmail02.blacknight.ie [81.17.254.11]) by outbound-smtp18.blacknight.com (Postfix) with ESMTPS id B26271C3A79 for ; Fri, 2 Oct 2020 11:19:53 +0100 (IST) Received: (qmail 4410 invoked from network); 2 Oct 2020 10:19:53 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 2 Oct 2020 10:19:53 -0000 Date: Fri, 2 Oct 2020 11:19:52 +0100 From: Mel Gorman To: Peter Zijlstra Cc: Michal Hocko , Uladzislau Rezki , Vlastimil Babka , LKML , RCU , linux-mm@kvack.org, Andrew Morton , "Paul E . McKenney" , Thomas Gleixner , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko Subject: Re: [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func. Message-ID: <20201002101952.GE3227@techsingularity.net> References: <20200918194817.48921-3-urezki@gmail.com> <38f42ca1-ffcd-04a6-bf11-618deffa897a@suse.cz> <20200929220742.GB8768@pc636> <795d6aea-1846-6e08-ac1b-dbff82dd7133@suse.cz> <20201001192626.GA29606@pc636> <20201002071123.GB20872@dhcp22.suse.cz> <20201002085014.GC3227@techsingularity.net> <20201002090729.GU2628@hirez.programming.kicks-ass.net> <20201002094502.GD3227@techsingularity.net> <20201002095858.GN2611@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20201002095858.GN2611@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Fri, Oct 02, 2020 at 11:58:58AM +0200, Peter Zijlstra wrote: > > It's enabled by default by enough distros that adding too many checks > > is potentially painful. Granted it would be missed by most benchmarking > > which tend to control allocations from userspace but a lot of performance > > problems I see are the "death by a thousand cuts" variety. > > Oh quite agreed, aka death by accounting. But if people are enabling > DEBUG options in production kernels, there's something wrong, no? > You'd think but historically I believe DEBUG_VM was enabled for some distributions because it made certain classes of problems easier to debug early. There is also a recent trend for enabling various DEBUG options for "hardening" even when they protect very specific corner cases or are for intended for kernel development. I've pushed back where I have an opinion that matters but it's generally corrosive. > Should we now go add CONFIG_REALLY_DEBUG_STAY_AWAY_ALREADY options? It's heading in that direction :( -- Mel Gorman SUSE Labs