On Thu, Oct 20, 2016 at 01:55:00PM +0200, Jan Kara wrote: > Hi Christoph, > > On Mon 17-10-16 12:26:57, Christoph Hellwig wrote: > > > Ping? I have ext4 DAX read & write path working with the iomap code but to > > > convert the fault path, I need this resolved. Are you OK with moving > > > iomap_begin() / iomap_end() calls outside of page lock / entry lock in the > > > fault path? > > > > Yes, that sounds fine. > > I've been looking into this some more and realized it's not as easy as I've > originally though. ->page_mkwrite callback is expected to return with the > page locked so locking it inside the iomap actor is really awkward (think > of situation when blocksize < pagesize). Since nobody currently has issues > with ->iomap_begin being sometimes called with page lock and sometimes > without, I don't think changing that would be worth the hassle. Just one > more question: Doesn't XFS have some lock ordering issues when > xfs_file_iomap_begin() gets called with page lock held from > iomap_page_mkwrite() for a file with extent size hints and thus we end up > in xfs_iomap_write_direct() with page lock held? We do a lot of stuff there > including transaction setup and such... Lock order in xfs is iolock->page lock->transaction->ilock, so what is being done in xfs_file_iomap_begin (transactions, ilock) is fine regardless of whether we hold the page locked or noti when called. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
