Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754727Ab0AFDUZ (ORCPT ); Tue, 5 Jan 2010 22:20:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754549Ab0AFDUY (ORCPT ); Tue, 5 Jan 2010 22:20:24 -0500 Received: from casper.infradead.org ([85.118.1.10]:59460 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753087Ab0AFDUY (ORCPT ); Tue, 5 Jan 2010 22:20:24 -0500 Date: Tue, 5 Jan 2010 19:22:43 -0800 From: Arjan van de Ven To: Christoph Lameter Cc: Peter Zijlstra , "Paul E. McKenney" , Peter Zijlstra , KAMEZAWA Hiroyuki , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "minchan.kim@gmail.com" , "hugh.dickins" , Nick Piggin , Ingo Molnar , Linus Torvalds Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault() Message-ID: <20100105192243.1d6b2213@infradead.org> In-Reply-To: References: <20100104182429.833180340@chello.nl> <20100104182813.753545361@chello.nl> <20100105054536.44bf8002@infradead.org> Organization: Intel X-Mailer: Claws Mail 3.7.3 (GTK+ 2.16.6; i586-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1438 Lines: 36 On Tue, 5 Jan 2010 09:17:11 -0600 (CST) Christoph Lameter wrote: > On Tue, 5 Jan 2010, Arjan van de Ven wrote: > > > while I appreciate the goal of reducing contention on this lock... > > wouldn't step one be to remove the page zeroing from under this > > lock? that's by far (easily by 10x I would guess) the most > > expensive thing that's done under the lock, and I would expect a > > first order of contention reduction just by having the zeroing of a > > page not done under the lock... > > The main issue is cacheline bouncing. mmap sem is a rw semaphore and > only held for read during a fault. depends on the workload; on a many-threads-java workload, you also get it for write quite a bit (lots of malloc/frees in userspace in addition to pagefaults).. at which point you do end up serializing on the zeroing. There's some real life real big workloads that show this pretty badly; so far the workaround is to have glibc batch up a lot of the free()s.. but that's just pushing it a little further out. > -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/