Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2993038AbXEBKw3 (ORCPT ); Wed, 2 May 2007 06:52:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S2993036AbXEBKw3 (ORCPT ); Wed, 2 May 2007 06:52:29 -0400 Received: from public.id2-vpn.continvity.gns.novell.com ([195.33.99.129]:43116 "EHLO gwia-smtp.id2.novell.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2993028AbXEBKw2 convert rfc822-to-8bit (ORCPT ); Wed, 2 May 2007 06:52:28 -0400 Message-Id: <463889A9.76E4.0078.0@novell.com> X-Mailer: Novell GroupWise Internet Agent 7.0.1 Date: Wed, 02 May 2007 11:52:57 +0100 From: "Jan Beulich" To: "Andi Kleen" , Cc: , Subject: Re: [patches] [PATCH] [28/34] i386: pte xchg optimization References: <20070430549.617098000@suse.de> <20070430155001.8525915209@wotan.suse.de> In-Reply-To: <20070430155001.8525915209@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1105 Lines: 25 >>> Andi Kleen 30.04.07 17:50 >>> > >From: Zachary Amsden > >In situations where page table updates need only be made locally, and there is >no cross-processor A/D bit races involved, we need not use the heavyweight >xchg instruction to atomically fetch and clear page table entries. Instead, >we can just read and clear them directly. I always wondered why the xchg is necessary here at all. If the process of tearing down a page table entry has started, other users of the mapped linear address are broken anyway - why is it necessary to still monitor the effect they may have on the A/D bits, unless this is a transient tear down? Checking for the uses of ptep_get_and_clear, I would judge that the use in change_pte_range() may in fact need the xchg, but the uses in vunmap_pte_range() and zap_pte_range() shouldn't. Jan - 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/