On Wed, Jul 28, 2010 at 10:08:44AM +0200, Tejun Heo wrote: > What I don't get here is if filesystems order requests already by > waiting for completions why do they use barriers at all? All they > need is flush request after all the preceding requests are known to be > complete. In fact for XFS I'm working on doing some bit of that, too, but it's not actually that easy. For one we don't actually have a non-barrier cache flush primitive currently, although the conversion of cache flushes to FS requests and the addition of REQ_FLUSH helps greatly with it. Second the usual primitive for log writes actually is a WRITE_FUA, that is a WRITE that needs to go to disk, without consequences to the rest of the cache. I've stared implementing that, including proper emulation for devices only supporting cache flushes but got stuck with the barrier machinery. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
