On Fri, Aug 07, 2015 at 04:25:52AM -0400, Ming Lei wrote: > On Fri, Aug 7, 2015 at 3:43 AM, Christoph Hellwig <h...@infradead.org> wrote: > > I really disagree with the per-cmd use_dio tracking. > > Could you explain it in a bit? > > > > > If we know at setup time that the loop device sector size is smaller > > than the sector size of the underlying device we should never allow > > dio, and othewise it should always work for data. > > Yes, that is just what I did in v7, and we can only do dio in case > of 512 byte sector size of backing device(not considering the > following patches from Hannes). > > When sector size of backing device isn't 512, most of transfer(buffered I/O > and normal dio) is still 4k aligned, that is why I suggest to use per-cmd > use_dio tracking. > > The patch avoids the race between buffered io and dio, doesn't it? > The introduced cost is trivial and most of times it needn't to wait for > completion of pending dio.
All block filesystems can do direct I/O on a _sector size_, not _block size_ boundary, e.g. for the typical setup of a 4k block size xfs/btrfs/ext4 file system on a 512 byte sector device you can do 512 byte aligned direct I/O. > > is no need for draining or mode checking for an fsync - FLUSH is always > > only guranteed to flush out I/O that has completed by the time it's > > issued. > > Could you point it out in the patch? Basically your lo_drain_pending_dio() functionality is not needed. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
