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[23.128.96.18]) by mx.google.com with ESMTP id w3si2273201ejy.651.2020.10.06.08.44.15; Tue, 06 Oct 2020 08:44:39 -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; dkim=pass header.i=@kernel.org header.s=default header.b=rQ6Zbe34; 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; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726012AbgJFPlF (ORCPT + 99 others); Tue, 6 Oct 2020 11:41:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:60042 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725769AbgJFPlF (ORCPT ); Tue, 6 Oct 2020 11:41:05 -0400 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) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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