On Thu, May 05, 2016 at 04:16:37PM +0200, Jan Kara wrote: > We cannot easily do this currently - the reason is that in several places we > wait for i_dio_count to drop to 0 (look for inode_dio_wait()) while > holding i_mutex to wait for all outstanding DIO / DAX IO. You'd break this > logic with this patch. > > If we indeed put all writes under i_mutex, this problem would go away but > as Dave explains in his email, we consciously do as much IO as we can > without i_mutex to allow reasonable scalability of multiple writers into > the same file. So the above should be fine for xfs, but you're telling me that ext4 is doing DAX I/O without any inode lock at all? In that case it's indeed not going to work. > The downside of that is that overwrites and writes vs reads are not atomic > wrt each other as POSIX requires. It has been that way for direct IO in XFS > case for a long time, with DAX this non-conforming behavior is proliferating > more. I agree that's not ideal but serializing all writes on a file is > rather harsh for persistent memory as well... For non-O_DIRECT I/O it's simply required.. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
