From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: [patch 1/3] add the fsblock layer Date: Mon, 25 Jun 2007 08:29:06 -0400 Message-ID: <20070625122906.GB12446@think.oraclecorp.com> References: <20070624014528.GA17609@wotan.suse.de> <20070624014613.GB17609@wotan.suse.de> <18046.63436.472085.535177@notabene.brown> <467F71C6.6040204@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Neil Brown , Nick Piggin , Linux Kernel Mailing List , Linux Memory Management List , linux-fsdevel@vger.kernel.org To: Nick Piggin Return-path: Received: from agminet01.oracle.com ([141.146.126.228]:18882 "EHLO agminet01.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752630AbXFYMcC (ORCPT ); Mon, 25 Jun 2007 08:32:02 -0400 Content-Disposition: inline In-Reply-To: <467F71C6.6040204@yahoo.com.au> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Mon, Jun 25, 2007 at 05:41:58PM +1000, Nick Piggin wrote: > Neil Brown wrote: > >On Sunday June 24, npiggin@suse.de wrote: > > > >> > >>+#define PG_blocks 20 /* Page has block mappings */ > >>+ > > > > > >I've only had a very quick look, but this line looks *very* wrong. > >You should be using PG_private. > > > >There should never be any confusion about whether ->private has > >buffers or blocks attached as the only routines that ever look in > >->private are address_space operations (or should be. I think 'NULL' > >is sometimes special cased, as in try_to_release_page. It would be > >good to do some preliminary work and tidy all that up). > > There is a lot of confusion, actually :) > But as you see in the patch, I added a couple more aops APIs, and > am working toward decoupling it as much as possible. It's pretty > close after the fsblock patch... however: > > > >Why do you think you need PG_blocks? > > Block device pagecache (buffer cache) has to be able to accept > attachment of either buffers or blocks for filesystem metadata, > and call into either buffer.c or fsblock.c based on that. > > If the page flag is really important, we can do some awful hack > like assuming the first long of the private data is flags, and > those flags will tell us whether the structure is a buffer_head > or fsblock ;) But for now it is just easier to use a page flag. The block device pagecache isn't special, and certainly isn't that much code. I would suggest keeping it buffer head specific and making a second variant that does only fsblocks. This is mostly to keep the semantics of PagePrivate sane, lets not fuzz the line. -chris