From: Nitin Gupta Subject: Re: [PATCH V3 0/8] Cleancache: overview Date: Sat, 24 Jul 2010 00:06:01 +0530 Message-ID: <4C49E111.2000106@vflare.org> References: <20100621231809.GA11111@ca-server1.us.oracle.com4C49468B.40307@vflare.org> <840b32ff-a303-468e-9d4e-30fc92f629f8@default 20100723140440.GA12423@infradead.org 364c83bd-ccb2-48cc-920d-ffcf9ca7df19@default> Reply-To: ngupta@vflare.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Christoph Hellwig , akpm@linux-foundation.org, Chris Mason , viro@zeniv.linux.org.uk, adilger@sun.com, tytso@mit.edu, mfasheh@suse.com, Joel Becker , matthew@wil.cx, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, ocfs2-devel@oss.oracle.com, linux-mm@kvack.org, jeremy@goop.org, JBeulich@novell.com, Kurt Hackel , npiggin@suse.de, Dave Mccracken , riel@redhat.com, avi@redhat.com, Konrad Wilk To: Dan Magenheimer Return-path: Received: from mail-pv0-f174.google.com ([74.125.83.174]:51428 "EHLO mail-pv0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751318Ab0GWSff (ORCPT ); Fri, 23 Jul 2010 14:35:35 -0400 In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On 07/23/2010 11:07 PM, Dan Magenheimer wrote: >> From: Dan Magenheimer >> Subject: RE: [PATCH V3 0/8] Cleancache: overview >> >>> From: Christoph Hellwig [mailto:hch@infradead.org] >>> Subject: Re: [PATCH V3 0/8] Cleancache: overview >>> >>> On Fri, Jul 23, 2010 at 06:58:03AM -0700, Dan Magenheimer wrote: >>>> CHRISTOPH AND ANDREW, if you disagree and your concerns have >>>> not been resolved, please speak up. >> >> Hi Christoph -- >> >> Thanks very much for the quick (instantaneous?) reply! >> >>> Anything that need modification of a normal non-shared fs is utterly >>> broken and you'll get a clear NAK, so the propsal before is a good >>> one. >> >> Unless/until all filesystems are 100% built on top of VFS, >> I have to disagree. Abstractions (e.g. VFS) are never perfect. > > After thinking about this some more, I can see a way > to enforce "opt-in" in the cleancache backend without > any changes to non-generic fs code. I think it's a horrible > hack and we can try it, but I expect fs maintainers > would prefer the explicit one-line-patch opt-in. > > 1) Cleancache backend maintains a list of "known working" > filesystems (those that have been tested). Checks against "known working list" indeed looks horrible. Isn't there any way to identify pagecache -> disk I/O boundaries which every filesystem obeys? I'm not yet sure but if this is doable, then we won't require such hacks. > > 2) Nitin's proposed changes pass the *sb as a parameter. > The string name of the filesystem type is available via > sb->s_type->name. This can be compared against > the "known working" list. > sb->s_magic could also be used, or better if we can somehow get rid of these checks :) > Using the sb pointer as a "handle" requires an extra > table search on every cleancache get/put/flush, > and fs/super.c changes are required for fs unmount > notification anyway (e.g. to call cleancache_flush_fs) > so I'd prefer to keep the cleancache_poolid addition > to the sb. I'll assume this is OK since this is in generic > fs code. > I will also try making changes to cleancache so it does not touch any fs specific code. Though IMHO one liners to fs-code should really be acceptable but unfortunately this doesn't seem to be the case. Maybe generic cleancache will have better chances. Thanks, Nitin