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[23.128.96.18]) by mx.google.com with ESMTP id pv21si811743ejb.44.2020.10.02.03.30.03; Fri, 02 Oct 2020 03:30:26 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387732AbgJBK3J (ORCPT + 99 others); Fri, 2 Oct 2020 06:29:09 -0400 Received: from outbound-smtp44.blacknight.com ([46.22.136.52]:60341 "EHLO outbound-smtp44.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726181AbgJBK3J (ORCPT ); Fri, 2 Oct 2020 06:29:09 -0400 X-Greylist: delayed 554 seconds by postgrey-1.27 at vger.kernel.org; Fri, 02 Oct 2020 06:29:08 EDT Received: from mail.blacknight.com (pemlinmail02.blacknight.ie [81.17.254.11]) by outbound-smtp44.blacknight.com (Postfix) with ESMTPS id B250BF80DF 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) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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