From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751499AbXBPHbz (ORCPT ); Fri, 16 Feb 2007 02:31:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751315AbXBPHby (ORCPT ); Fri, 16 Feb 2007 02:31:54 -0500 Received: from smtp103.mail.mud.yahoo.com ([209.191.85.213]:30600 "HELO smtp103.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751499AbXBPHbx (ORCPT ); Fri, 16 Feb 2007 02:31:53 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:X-YMail-OSG:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=j0937vSADIoSpw0FoYFQQ5jfSKPtCrY4plYuBV0bWevljH4hWsfZvFfrR6Hm2/zWhGZkYPqxyqjCBfbFmgklcMJ5L2AhSb5gLae9UOnKn3Jnh6mB5ErPXe19BQJhxQ3XfWRe4Izpwnix0PaqZaMgYW/9s/Op3hZ77NTSpHms/qc= ; X-YMail-OSG: gA3f6cQVM1noRX8nWSff8eSWT2qvYJ22.ra2ct7gMvsEeZV09Oor.5InAH5TdZ4TC2qGrFgAON7fonBk5qRPJzGPKJcGkVa_2jKsAJmXxNCYy4FQ4PsiXL3bWarWJk95rPXqwqHdr_yakMQ- Message-ID: <45D55DC2.3070703@yahoo.com.au> Date: Fri, 16 Feb 2007 18:31:14 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20051007 Debian/1.7.12-1 X-Accept-Language: en MIME-Version: 1.0 To: Andrew Morton CC: Jeremy Fitzhardinge , Andi Kleen , linux-kernel@vger.kernel.org, virtualization@lists.osdl.org, xen-devel@lists.xensource.com, Chris Wright , Zachary Amsden , Ian Pratt , Christian Limpach , Christoph Lameter , Linux Memory Management , David Rientjes Subject: Re: [patch 11/21] Xen-paravirt: Add apply_to_page_range() which applies a function to a pte range. References: <20070216022449.739760547@goop.org> <20070216022531.344125142@goop.org> <20070215223727.6819f962.akpm@linux-foundation.org> In-Reply-To: <20070215223727.6819f962.akpm@linux-foundation.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > On Thu, 15 Feb 2007 18:25:00 -0800 Jeremy Fitzhardinge wrote: > > >>Add a new mm function apply_to_page_range() which applies a given >>function to every pte in a given virtual address range in a given mm >>structure. This is a generic alternative to cut-and-pasting the Linux >>idiomatic pagetable walking code in every place that a sequence of >>PTEs must be accessed. >> >>Although this interface is intended to be useful in a wide range of >>situations, it is currently used specifically by several Xen >>subsystems, for example: to ensure that pagetables have been allocated >>for a virtual address range, and to construct batched special >>pagetable update requests to map I/O memory (in ioremap()). > > > There was some discussion about this sort of thing last week. The > consensus was that it's better to run the callback against a whole pmd's > worth of ptes, mainly to amortise the callback's cost (a lot). > > It was implemented in > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.20/2.6.20-mm1/broken-out/smaps-extract-pmd-walker-from-smaps-code.patch Speaking of that patch, I missed the discussion, but I'd hope it doesn't go upstream in its current form. We now have one way of walking range of ptes. The code may be duplicated a few times, but it is simple, we know how it works, and it is easy to get right because everyone does the same thing. We used to have about a dozen slightly different ways of doing this until Hugh spent the effort to standardise it all. Isn't it nice? If we want an ever-so-slightly lower performing interface for those paths that don't care to count every cycle -- which I think is a fine idea BTW -- it should be implemented in mm/memory.c and it should use our standard form of pagetable walking. -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com