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=-6.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 5161BC4727E for ; Tue, 6 Oct 2020 15:41:09 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A1FC320789 for ; Tue, 6 Oct 2020 15:41:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="rQ6Zbe34" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A1FC320789 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9BB2E6B005C; Tue, 6 Oct 2020 11:41:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 945426B005D; Tue, 6 Oct 2020 11:41:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 80BF36B0062; Tue, 6 Oct 2020 11:41:07 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 50F916B005C for ; Tue, 6 Oct 2020 11:41:07 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id A6C96362C for ; Tue, 6 Oct 2020 15:41:06 +0000 (UTC) X-FDA: 77341914132.16.teeth88_1a00bbe271c7 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin16.hostedemail.com (Postfix) with ESMTP id 812FB100E44F7 for ; Tue, 6 Oct 2020 15:41:06 +0000 (UTC) X-HE-Tag: teeth88_1a00bbe271c7 X-Filterd-Recvd-Size: 4799 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf05.hostedemail.com (Postfix) with ESMTP for ; Tue, 6 Oct 2020 15:41:05 +0000 (UTC) Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CB6DD206F7; Tue, 6 Oct 2020 15:41:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601998864; bh=5zcZJgeXWMZfqD9CHwUsl8a8Af1+R/wD5uulfCzXK5Q=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=rQ6Zbe3409jzMfKdP5zm0LSY4ZRePO1jIu3iKr7VIaprlbkkT7JbwKynwMM+0Gn/K ANeSzK6ifLHXcdbfk28NmNQ3K+VJIBQQjg7FM/zHoOmCckK7iPfrWgXOH0Y9wMKTF/ HdMdpN6fglz4ja9ygnAMqSZLOj4hALgifxu977k8= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 73DD93520A89; Tue, 6 Oct 2020 08:41:04 -0700 (PDT) Date: Tue, 6 Oct 2020 08:41:04 -0700 From: "Paul E. McKenney" To: Mel Gorman Cc: Peter Zijlstra , Michal Hocko , Uladzislau Rezki , Vlastimil Babka , LKML , RCU , linux-mm@kvack.org, Andrew Morton , 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: <20201006154104.GH29330@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <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> <20201002101952.GE3227@techsingularity.net> <20201002144120.GI29330@paulmck-ThinkPad-P72> <20201006100334.GK3227@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201006100334.GK3227@techsingularity.net> User-Agent: Mutt/1.9.4 (2018-02-28) 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 Tue, Oct 06, 2020 at 11:03:34AM +0100, Mel Gorman wrote: > On Fri, Oct 02, 2020 at 07:41:20AM -0700, Paul E. McKenney wrote: > > On Fri, Oct 02, 2020 at 11:19:52AM +0100, Mel Gorman wrote: > > > 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 :( > > > > Given that you guys have just reiterated yet again that you are very > > unhappy with either a GFP_ flag or a special function like the one that > > Peter Zijlstra put together, it would be very helpful if you were to at > > least voice some level of support for Thomas Gleixner's patchset, which, > > if accepted, will allow me to solve at least 50% of the problem. > > I read through the series and didn't find anything problematic that > had not been covered already. Minimally, avoiding surprises about what > preemptible() means in different contexts is nice. While I have not > run it through a test grid to check, I'd be very surprised if this was > problematic from a performance perspective on a preempt-disabled kernels. > Last I checked, the difference between PREEMPT_NONE and PREEMPT_VOLUNTARY > was less than 2% *at worst* and I don't think that was due to the preempt > accounting. Thank you, Mel! Thanx, Paul