On Wednesday 21 September 2005 20:04, Jeff Dike wrote: > On Wed, Sep 21, 2005 at 05:49:43PM +0200, Blaisorblade wrote: [...] > > Don't think it's reasonable to expect this. I think that filesystems like > > ext2 will never produce write barriers - they are needed for journaled > > FS's.
> I thought your point was to rely on the block layer to order overlapping > writes for us. 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. For the buffer cache (i.e. fs metadata) it may still hold, but I'm not sure at all. Not that it matters for us - we can't depend on it anyway. No, I was thinking to you enforcing ordering to comply to what journaled filesystems expect. 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). > It sounded reasonable to me :-) > Jeff -- 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 [email protected] https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
