From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755470AbYJOSah (ORCPT ); Wed, 15 Oct 2008 14:30:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753343AbYJOSaa (ORCPT ); Wed, 15 Oct 2008 14:30:30 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:49010 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753243AbYJOSa3 (ORCPT ); Wed, 15 Oct 2008 14:30:29 -0400 Date: Wed, 15 Oct 2008 11:29:32 -0700 (PDT) From: Linus Torvalds To: Nick Piggin cc: Matt Mackall , Pekka Enberg , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [rfc] SLOB memory ordering issue In-Reply-To: <200810160512.28443.nickpiggin@yahoo.com.au> Message-ID: References: <200810160334.13082.nickpiggin@yahoo.com.au> <200810160445.28781.nickpiggin@yahoo.com.au> <200810160512.28443.nickpiggin@yahoo.com.au> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 16 Oct 2008, Nick Piggin wrote: > > When I said "I'd really hate to add a branch to the slab fastpath", it > wasn't a tacit acknowlegement that the barrier is the only way to go, > if it sounded that way. > > I meant: I'd *really* hate to add a branch to the slab fastpath :) Well, quite frankly, your choice of subject line and whole point of argument may have confused me. You started out - and continue to - make this sound like it's a SLAB/SLOB/SLUB issue. It's not. I agree there is quite likely memory ordering issues - possibly old ones, but quite possibly also ones that have just happened fairly recently as we've done more unlocked lookups - and all I've ever disagreed with is how you seem to have mixed this up with the allocator. And I still don't understand why you even _mention_ the slab fastpath. It seems totally immaterial. Linus