From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Francis Moreau" Subject: Re: PG_updatodate vs BH_updatodate Date: Mon, 24 Nov 2008 17:42:48 +0100 Message-ID: <38b2ab8a0811240842y5032ab6fhad5201333c47af5d@mail.gmail.com> References: <20081123041938.GW3186@webber.adilger.int> <20081123122124.GH5707@parisc-linux.org> <20081124155633.GB3051@logfs.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: "Matthew Wilcox" , "Andreas Dilger" , linux-fsdevel@vger.kernel.org To: "=?ISO-8859-1?Q?J=F6rn_Engel?=" Return-path: Received: from ug-out-1314.google.com ([66.249.92.174]:41058 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753355AbYKXQmv convert rfc822-to-8bit (ORCPT ); Mon, 24 Nov 2008 11:42:51 -0500 Received: by ug-out-1314.google.com with SMTP id 39so795110ugf.37 for ; Mon, 24 Nov 2008 08:42:49 -0800 (PST) In-Reply-To: <20081124155633.GB3051@logfs.org> Content-Disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Mon, Nov 24, 2008 at 4:56 PM, J=F6rn Engel wrote: > On Sun, 23 November 2008 21:14:47 +0100, Francis Moreau wrote: >> Matthew Wilcox writes: >> > On Sun, Nov 23, 2008 at 01:14:52PM +0100, Francis Moreau wrote: >> > >> >> Are there any cases where a page can be partially uptodate ? >> > >> > Consider a filesystem with 1k blocks and a system with a page size= of 4k. >> > You have a buffer_head for each of the four blocks that are being = kept >> > in the page, and you want to track their dirty state independently= =2E >> >> Sorry but I'm confused since you're taking about the dirty state >> (tracked by BH_Dirty bit) and I was taking about the uptodate state >> (tracked by BH_Uptodate bit). > > Think page cache, except that the granularity is not pages but 1k > blocks. If your filesystem wants to read an indirect block, 1k is re= ad > into the cache, the other 3k (or 63k) of the page remain as they were= =2E > So if I understand you correctly, we can update a page cache partially only when the filesystems needs to read its metadata. But not when reading a page of = data. That's pretty what Matthew answered I think but I'm confused about the dirty bit of the buffer header he mentioned. Thanks --=20 =46rancis -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html