From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sc8-sf-mx1-b.sourceforge.net ([10.3.1.91] helo=mail.sourceforge.net) by sc8-sf-list1.sourceforge.net with esmtp (Exim 4.30) id 1EIY3j-0003Iu-Jq for user-mode-linux-devel@lists.sourceforge.net; Thu, 22 Sep 2005 13:52:47 -0700 Received: from smtp004.mail.ukl.yahoo.com ([217.12.11.35]) by mail.sourceforge.net with smtp (Exim 4.44) id 1EIY3h-0006k5-Vv for user-mode-linux-devel@lists.sourceforge.net; Thu, 22 Sep 2005 13:52:47 -0700 From: Blaisorblade Subject: Re: [uml-devel] Review needed for ubd fixes References: <200509172245.j8HMjqJD009056@ccure.user-mode-linux.org> <200509212106.39169.blaisorblade@yahoo.it> <20050921204507.GA9918@ccure.user-mode-linux.org> In-Reply-To: <20050921204507.GA9918@ccure.user-mode-linux.org> MIME-Version: 1.0 Content-Disposition: inline Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <200509222251.31918.blaisorblade@yahoo.it> Sender: user-mode-linux-devel-admin@lists.sourceforge.net Errors-To: user-mode-linux-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Id: The user-mode Linux development list List-Post: List-Help: List-Subscribe: , List-Archive: Date: Thu, 22 Sep 2005 22:51:31 +0200 To: Jeff Dike Cc: user-mode-linux-devel@lists.sourceforge.net, Bodo Stroesser On Wednesday 21 September 2005 22:45, Jeff Dike wrote: > On Wed, Sep 21, 2005 at 09:06:38PM +0200, Blaisorblade wrote: > > The block layer is supposed to merge as far as possible overlapping > > writes, that's reasonable, but not dependable. Say it gets the > > overlapping request *after* it sent the first one - we'll see both. Also, > > this is trivially true for output done through page cache, but for the > > rest I don't know if explicit merging is implemented. > > Yeah, I'm concerned about O_DIRECT. Also, what happens when we write a > page to disk, and immediately afterwards, it gets dirty again and written > again? Is there a barrier between the two? > > > No, I was thinking to you enforcing ordering to comply to what journaled > > filesystems expect. > > Yeah, but there's more ordering than that. > > > Btw: even when we aren't using COW, we're supposed to do writes in the > > order the fs passed them to us - at least when write barriers are > > explicitly sent (don't know if there's something to care normally - I > > know this as a LWN.net reader, not as an hacker in this area). > > We get requests from the block layer, not the fs. And physical disks are > allowed to reorder requests, so I think there is some flexibility there. I expect the FS to send the barriers - they don't make sense otherwise. In fact, grep -i barrier fs/jbd/*.c gives some results, which point to BH_Ordered. And after grepping it in reiserfs, I found that fs/buffer.c:submit_bh() cares about it (i.e. looks at the buffer head and sees if it is ordered), and sends it down to the elevator. -- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade ___________________________________ Yahoo! Mail: gratis 1GB per i messaggi e allegati da 10MB http://mail.yahoo.it ------------------------------------------------------- SF.Net email is sponsored by: Tame your development challenges with Apache's Geronimo App Server. Download it for free - -and be entered to win a 42" plasma tv or your very own Sony(tm)PSP. Click here to play: http://sourceforge.net/geronimo.php _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel