From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756109AbaA1Xwv (ORCPT ); Tue, 28 Jan 2014 18:52:51 -0500 Received: from www.sr71.net ([198.145.64.142]:36133 "EHLO blackbird.sr71.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755862AbaA1Xwu (ORCPT ); Tue, 28 Jan 2014 18:52:50 -0500 Message-ID: <52E842CF.7090102@sr71.net> Date: Tue, 28 Jan 2014 15:52:47 -0800 From: Dave Hansen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Andrew Morton CC: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cl@linux-foundation.org, penberg@kernel.org, mpm@selenic.com, pshelar@nicira.com, Wu Fengguang Subject: Re: [PATCH] mm: slub: fix page->_count corruption (again) References: <20140128231722.E7387E6B@viggo.jf.intel.com> <20140128152956.d5659f56ae279856731a1ac5@linux-foundation.org> In-Reply-To: <20140128152956.d5659f56ae279856731a1ac5@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/28/2014 03:29 PM, Andrew Morton wrote: > On Tue, 28 Jan 2014 15:17:22 -0800 Dave Hansen wrote: > This code is borderline insane. No argument here. > Yes, struct page is special and it's worth spending time and doing > weird things to optimise it. But sheesh. > > An alternative is to make that cmpxchg quietly go away. Is it more > trouble than it is worth? It has measurable performance benefits, and the benefits go up as the cost of en/disabling interrupts goes up (like if it takes you a hypercall). Fengguang, could you run a set of tests for the top patch in this branch to see if we'd be giving much up by axing the code? https://github.com/hansendc/linux/tree/slub-nocmpxchg-for-Fengguang-20140128 I was talking with one of the distros about turning it off as well. They mentioned that they saw a few performance regressions when it was turned off. I'll share details when I get them.