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Re: [PATCH 5/5] xfs: using generic_file_direct_write() is unnecessary

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 5/5] xfs: using generic_file_direct_write() is unnecessary
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Fri, 10 Apr 2015 16:22:22 -0400
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1428673080-23052-6-git-send-email-david@xxxxxxxxxxxxx>
References: <1428673080-23052-1-git-send-email-david@xxxxxxxxxxxxx> <1428673080-23052-6-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.23 (2014-03-12)
On Fri, Apr 10, 2015 at 11:38:00PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
> 
> generic_file_direct_write() does all sorts of things to make DIO
> work "sorta ok" with mixed buffered IO workloads. We already do
> most of this work in xfs_file_aio_dio_write() because of the locking
> requirements, so there's only a couple of things it does for us.
> 
> The first thing is that it does a page cache invalidation after the
> ->direct_IO callout. This can easily be added to the XFS code.
> 
> The second thing it does is that if data was written, it updates the
> iov_iter structure to reflect the data written, and then does EOF
> size updates if necessary. For XFS, these EOF size updates are now
> not necessary, as we do them safely and race-free in IO completion
> context. That leaves just the iov_iter update, and that's also exily
> moved to the XFS code.
> 
> The result is that we don't need to call
> generic_file_direct_write(), and hence remove a redundant buffered
> writeback call and a redundant page cache invalidation call from the
> DIO submission path. We also remove a racy EOF size update, and make
> the DIO submission code in XFS much easier to follow. Wins all
> round, really.
> 
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---

Seems fine to me:

Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>

>  fs/xfs/xfs_file.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 7b872f4..7182cd2 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -665,6 +665,8 @@ xfs_file_dio_aio_write(
>       int                     iolock;
>       size_t                  count = iov_iter_count(from);
>       loff_t                  pos = iocb->ki_pos;
> +     loff_t                  end;
> +     struct iov_iter         data;
>       struct xfs_buftarg      *target = XFS_IS_REALTIME_INODE(ip) ?
>                                       mp->m_rtdev_targp : mp->m_ddev_targp;
>  
> @@ -704,10 +706,11 @@ xfs_file_dio_aio_write(
>       if (ret)
>               goto out;
>       iov_iter_truncate(from, count);
> +     end = pos + count - 1;
>  
>       if (mapping->nrpages) {
>               ret = filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
> -                                                 pos, pos + count - 1);
> +                                                pos, end);
>               if (ret)
>                       goto out;
>               /*
> @@ -717,7 +720,7 @@ xfs_file_dio_aio_write(
>                */
>               ret = invalidate_inode_pages2_range(VFS_I(ip)->i_mapping,
>                                       pos >> PAGE_CACHE_SHIFT,
> -                                     (pos + count - 1) >> PAGE_CACHE_SHIFT);
> +                                     end >> PAGE_CACHE_SHIFT);
>               WARN_ON_ONCE(ret);
>               ret = 0;
>       }
> @@ -734,8 +737,22 @@ xfs_file_dio_aio_write(
>       }
>  
>       trace_xfs_file_direct_write(ip, count, iocb->ki_pos, 0);
> -     ret = generic_file_direct_write(iocb, from, pos);
>  
> +     data = *from;
> +     ret = mapping->a_ops->direct_IO(WRITE, iocb, &data, pos);
> +
> +     /* see generic_file_direct_write() for why this is necessary */
> +     if (mapping->nrpages) {
> +             invalidate_inode_pages2_range(mapping,
> +                                           pos >> PAGE_CACHE_SHIFT,
> +                                           end >> PAGE_CACHE_SHIFT);
> +     }
> +
> +     if (ret > 0) {
> +             pos += ret;
> +             iov_iter_advance(from, ret);
> +             iocb->ki_pos = pos;
> +     }
>  out:
>       xfs_rw_iunlock(ip, iolock);
>  
> -- 
> 2.0.0
> 
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