Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932656AbWLMKgO (ORCPT ); Wed, 13 Dec 2006 05:36:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932657AbWLMKgO (ORCPT ); Wed, 13 Dec 2006 05:36:14 -0500 Received: from elvis.mu.org ([192.203.228.196]:57166 "EHLO elvis.mu.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932656AbWLMKgN (ORCPT ); Wed, 13 Dec 2006 05:36:13 -0500 Message-ID: <457FD777.9040703@FreeBSD.org> Date: Wed, 13 Dec 2006 02:35:35 -0800 From: Suleiman Souhlal User-Agent: Mozilla Thunderbird 1.0.7 (X11/20051204) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andrew Morton CC: Peter Zijlstra , linux-kernel@vger.kernel.org, balbir@in.ibm.com, csturtiv@sgi.com, daw@sgi.com, guillaume.thouvenin@bull.net, jlan@sgi.com, nagar@watson.ibm.com, tee@sgi.com Subject: Re: [patch 03/13] io-accounting: write accounting References: <200612081152.kB8BqQvb019756@shell0.pdx.osdl.net> <457FBDBE.10102@FreeBSD.org> <20061213005954.e2d32446.akpm@osdl.org> In-Reply-To: <20061213005954.e2d32446.akpm@osdl.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1509 Lines: 38 Andrew Morton wrote: > On Wed, 13 Dec 2006 00:45:50 -0800 > Suleiman Souhlal wrote: > > >>akpm@osdl.org wrote: >> >>>From: Andrew Morton >>> >>>Accounting writes is fairly simple: whenever a process flips a page from clean >>>to dirty, we accuse it of having caused a write to underlying storage of >>>PAGE_CACHE_SIZE bytes. >> >>On architectures where dirtying a page doesn't cause a page fault (like i386), couldn't you end up billing the wrong process (in fact, I think that even on other archituctures set_page_dirty() doesn't get called immediately in the page fault handler)? > > > Yes, that would be a problem in 2.6.18 and earlier. > > In 2.6.19 and later, we do take a fault when transitioning a page from > pte-clean to pte-dirty. That was done to get the dirty-page accounting > right - to avoid the all-of-memory-is-dirty-but-the-kernel-doesn't-know-it > problem. Ah yes indeed. I'm unable to keep up with all the new developments. :-( However, if my understanding of this code is correct, it seems that the page fault is only done for shared writable VMAs, so you still can't rely on set_page_dirty() always being called by the process that dirtied the page in the first place. Am I wrong? -- Suleiman - 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/