Re: [PATCH 04/27] xfs: don't use speculative prealloc for small files

Dave Chinner
2013-06-13T00:51:00Z

On Wed, Jun 12, 2013 at 12:10:00PM -0400, Brian Foster wrote:
> On 06/12/2013 06:22 AM, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> >
> ...
> > ---
> > fs/xfs/xfs_iomap.c | 13 +++++++++++++
> > 1 file changed, 13 insertions(+)
> >
> > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> > index 8f8aaee..14be676 100644
> > --- a/fs/xfs/xfs_iomap.c
> > +++ b/fs/xfs/xfs_iomap.c
> > @@ -284,6 +284,15 @@ xfs_iomap_eof_want_preallocate(
> > return 0;
> >
> > /*
> > + * If the file is smaller than the minimum prealloc and we are using
> > + * dynamic preallocation, don't do any preallocation at all as it is
> > + * likely this is the only write to the file that is going to be done.
> > + */
> > + if (!(mp->m_flags & XFS_MOUNT_DFLT_IOSIZE) &&
> > + XFS_ISIZE(ip) < mp->m_writeio_blocks)
> > + return 0;
> > +
>
> I stuck this on a box, got a 64k prealloc on an 8k file and then noticed
> this was comparing inode size against a block count. This should
> probably be:
>
> XFS_ISIZE(ip) < XFS_FSB_TO_B(mp, mp->m_writeio_blocks)
>
> Given that, we avoid preallocs entirely until the file size reaches the
> minimum write size (assuming dynamic prealloc mode).

Doh! Will fix.

Cheers

Dave.
--
Dave Chinner
david@fromorbit.com