From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: Dirtiable inode bdi default != sb bdi btrfs Date: Thu, 30 Sep 2010 02:06:41 +0200 Message-ID: <20100930000641.GA27865@lst.de> References: <4C9AA546.6050201@cesarb.net> <20100923123849.8975fe47.akpm@linux-foundation.org> <20100927222548.GG3610@quack.suse.cz> <20100927225452.GG4270@think> <20100929081936.GA23322@lst.de> <20100929121808.GB3290@quack.suse.cz> <20100929141006.GB7439@lst.de> <20100929233806.GB12707@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , Chris Mason , Cesar Eduardo Barros , Andrew Morton , linux-kernel@vger.kernel.org, Jens Axboe , linux-btrfs@vger.kernel.org, Alexander Viro , linux-fsdevel@vger.kernel.org, stable@kernel.org, Jens Axboe , Micha?? Piotrowski , Chuck Ebbert , kernel@lists.fedoraproject.org, linux-mtd@lists.infradead.org, David Woodhouse To: Jan Kara Return-path: Content-Disposition: inline In-Reply-To: <20100929233806.GB12707@quack.suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, Sep 30, 2010 at 01:38:07AM +0200, Jan Kara wrote: > > No. For one thing we don't need any exception for correctnes alone - > > even the block device variant would work fine with the default case. > Here I don't agree. If you don't have some kind of exception, sb->s_bdi > for both "block" and "mtd_inodefs" filesystems points to > noop_backing_dev_info and you get no writeback for that one. So it isn't > just a performance issue but also a correctness one. Indeed - for internal filesystems that require writeback the change causes trouble if they haven't registered a s_bdi. But for all user visible filesystems that doesn't happen as we require s_bdi for sync or even unmounts to work.