From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH 1/5] Forking ext4 filesystem from ext3 filesystem Date: Thu, 10 Aug 2006 13:27:20 -0700 Message-ID: <20060810132720.4d9fced4.akpm@osdl.org> References: <1155172622.3161.73.camel@localhost.localdomain> <20060809233914.35ab8792.akpm@osdl.org> <44DB8036.5020706@us.ibm.com> <44DB936D.2080909@garzik.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org, cmm@us.ibm.com, ext2-devel@lists.sourceforge.net, Badari Pulavarty , linux-kernel@vger.kernel.org Return-path: To: Jeff Garzik In-Reply-To: <44DB936D.2080909@garzik.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: ext2-devel-bounces@lists.sourceforge.net Errors-To: ext2-devel-bounces@lists.sourceforge.net List-Id: linux-fsdevel.vger.kernel.org On Thu, 10 Aug 2006 16:13:33 -0400 Jeff Garzik wrote: > The sooner we kill buffer heads and use submit_bio(), the better :) A buffer_head is a caching entity and a bio is an IO container. They're quite separate concepts. A buffer_head is the kernel's sole abstraction of a disk block. Filesystems use disk blocks a lot, and they need such an abstraction. If one was to replace buffer_heads with direct-to-BIO operations then the filesytem would need to internally track the mapping from page+offset+length -> disk block and it would need to internally track the page+offset+length<->disk block coherency state and it would need to internally perform serialisation of access to each page+offset+length hunk of pagecache and etc and etc and etc. Create a data structure with which to do all that and voila, buffer_heads reinvented. ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642