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Re: [PATCH 7/8] xfs: add DAX IO path support

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [PATCH 7/8] xfs: add DAX IO path support
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 16 Apr 2015 18:54:02 +1000
Cc: xfs@xxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, willy@xxxxxxxxxxxxxxx, jack@xxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20150406174913.GE58965@xxxxxxxxxxxxxxx>
References: <1427194266-2885-1-git-send-email-david@xxxxxxxxxxxxx> <1427194266-2885-8-git-send-email-david@xxxxxxxxxxxxx> <20150406174913.GE58965@xxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Apr 06, 2015 at 01:49:14PM -0400, Brian Foster wrote:
> On Tue, Mar 24, 2015 at 09:51:05PM +1100, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > 
> > DAX does not do buffered IO (can't buffer direct access!) and hence
> > all read/write IO is vectored through the direct IO path.  Hence we
> > need to add the DAX IO path callouts to the direct IO
> > infrastructure.
> > 
> > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> > ---
> >  fs/xfs/xfs_aops.c | 35 +++++++++++++++++++++++++++--------
> >  1 file changed, 27 insertions(+), 8 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> > index 3fc5052..97979e9 100644
> > --- a/fs/xfs/xfs_aops.c
> > +++ b/fs/xfs/xfs_aops.c
> > @@ -1559,6 +1559,30 @@ xfs_end_io_direct_write(
> >     }
> >  }
> >  
> > +static inline ssize_t
> > +xfs_vm_do_dio(
> > +   struct inode            *inode,
> > +   int                     rw,
> > +   struct kiocb            *iocb,
> > +   struct iov_iter         *iter,
> > +   loff_t                  offset,
> > +   void                    (*endio)(struct kiocb   *iocb,
> > +                                    loff_t         offset,
> > +                                    ssize_t        size,
> > +                                    void           *private),
> > +   int                     flags)
> > +{
> > +   struct block_device     *bdev;
> > +
> > +   if (IS_DAX(inode))
> > +           return dax_do_io(rw, iocb, inode, iter, offset,
> > +                            xfs_get_blocks_direct, endio, 0);
> > +
> 
> I assume this is supposed to be get_blocks_direct and not
> get_blocks_dax, based on the I/O codepath. The naming is starting to get
> a little confusing though. xfs_get_blocks_dax() implies to me that it's
> for any DAX I/O, but we only appear to use it internally for
> truncate/zeroing/mmap and such. Alas, I can't think of a better name atm
> and the code seems Ok to me:

xfs_get_blocks_dax is now gone as there is no difference between
the block mapping of DAX and direct IO....

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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