Re: [PATCH 25/34] xfs: remove xfs_reflink_trim_irec_to_next_cow

[Brian Foster <bfoster@redhat.com>]

On Wed, May 23, 2018 at 04:43:48PM +0200, Christoph Hellwig wrote:
> In the only caller we just did a lookup in the COW extent tree for
> the same offset.  Reuse that result and save a lookup, as well as
> shortening the ilock hold time.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/xfs_aops.c    | 25 +++++++++++++++++--------
>  fs/xfs/xfs_reflink.c | 33 ---------------------------------
>  fs/xfs/xfs_reflink.h |  2 --
>  3 files changed, 17 insertions(+), 43 deletions(-)
> 
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index a4b4a7037deb..354d26d66c12 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -383,11 +383,12 @@ xfs_map_blocks(
>  	struct xfs_inode	*ip = XFS_I(inode);
>  	struct xfs_mount	*mp = ip->i_mount;
>  	ssize_t			count = i_blocksize(inode);
> -	xfs_fileoff_t		offset_fsb, end_fsb;
> +	xfs_fileoff_t		offset_fsb, end_fsb, cow_fsb = 0;

cow_fsb should probably be initialized to NULLFSBLOCK rather than 0.
With that, you also shouldn't need cow_valid. Otherwise looks Ok to me.

Brian

>  	int			whichfork = XFS_DATA_FORK;
>  	struct xfs_iext_cursor	icur;
>  	int			error = 0;
>  	int			nimaps = 1;
> +	bool			cow_valid = false;
>  
>  	if (XFS_FORCED_SHUTDOWN(mp))
>  		return -EIO;
> @@ -407,8 +408,11 @@ xfs_map_blocks(
>  	 * it directly instead of looking up anything in the data fork.
>  	 */
>  	if (xfs_is_reflink_inode(ip) &&
> -	    xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, imap) &&
> -	    imap->br_startoff <= offset_fsb) {
> +	    xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, imap)) {
> +		cow_fsb = imap->br_startoff;
> +		cow_valid = true;
> +	}
> +	if (cow_valid && cow_fsb <= offset_fsb) {
>  		xfs_iunlock(ip, XFS_ILOCK_SHARED);
>  		/*
>  		 * Truncate can race with writeback since writeback doesn't
> @@ -430,6 +434,10 @@ xfs_map_blocks(
>  
>  	error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
>  				imap, &nimaps, XFS_BMAPI_ENTIRE);
> +	xfs_iunlock(ip, XFS_ILOCK_SHARED);
> +	if (error)
> +		return error;
> +
>  	if (!nimaps) {
>  		/*
>  		 * Lookup returns no match? Beyond eof? regardless,
> @@ -451,16 +459,17 @@ xfs_map_blocks(
>  		 * is a pending CoW reservation before the end of this extent,
>  		 * so that we pick up the COW extents in the next iteration.
>  		 */
> -		xfs_reflink_trim_irec_to_next_cow(ip, offset_fsb, imap);
> +		if (cow_valid &&
> +		    cow_fsb < imap->br_startoff + imap->br_blockcount) {
> +			imap->br_blockcount = cow_fsb - imap->br_startoff;
> +			trace_xfs_reflink_trim_irec(ip, imap);
> +		}
> +
>  		if (imap->br_state == XFS_EXT_UNWRITTEN)
>  			*type = XFS_IO_UNWRITTEN;
>  		else
>  			*type = XFS_IO_OVERWRITE;
>  	}
> -	xfs_iunlock(ip, XFS_ILOCK_SHARED);
> -	if (error)
> -		return error;
> -
>  done:
>  	switch (*type) {
>  	case XFS_IO_HOLE:
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 8e5eb8e70c89..ff76bc56ff3d 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -484,39 +484,6 @@ xfs_reflink_allocate_cow(
>  	return error;
>  }
>  
> -/*
> - * Trim an extent to end at the next CoW reservation past offset_fsb.
> - */
> -void
> -xfs_reflink_trim_irec_to_next_cow(
> -	struct xfs_inode		*ip,
> -	xfs_fileoff_t			offset_fsb,
> -	struct xfs_bmbt_irec		*imap)
> -{
> -	struct xfs_ifork		*ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
> -	struct xfs_bmbt_irec		got;
> -	struct xfs_iext_cursor		icur;
> -
> -	if (!xfs_is_reflink_inode(ip))
> -		return;
> -
> -	/* Find the extent in the CoW fork. */
> -	if (!xfs_iext_lookup_extent(ip, ifp, offset_fsb, &icur, &got))
> -		return;
> -
> -	/* This is the extent before; try sliding up one. */
> -	if (got.br_startoff < offset_fsb) {
> -		if (!xfs_iext_next_extent(ifp, &icur, &got))
> -			return;
> -	}
> -
> -	if (got.br_startoff >= imap->br_startoff + imap->br_blockcount)
> -		return;
> -
> -	imap->br_blockcount = got.br_startoff - imap->br_startoff;
> -	trace_xfs_reflink_trim_irec(ip, imap);
> -}
> -
>  /*
>   * Cancel CoW reservations for some block range of an inode.
>   *
> diff --git a/fs/xfs/xfs_reflink.h b/fs/xfs/xfs_reflink.h
> index 15a456492667..e8d4d50c629f 100644
> --- a/fs/xfs/xfs_reflink.h
> +++ b/fs/xfs/xfs_reflink.h
> @@ -32,8 +32,6 @@ extern int xfs_reflink_allocate_cow(struct xfs_inode *ip,
>  		struct xfs_bmbt_irec *imap, bool *shared, uint *lockmode);
>  extern int xfs_reflink_convert_cow(struct xfs_inode *ip, xfs_off_t offset,
>  		xfs_off_t count);
> -extern void xfs_reflink_trim_irec_to_next_cow(struct xfs_inode *ip,
> -		xfs_fileoff_t offset_fsb, struct xfs_bmbt_irec *imap);
>  
>  extern int xfs_reflink_cancel_cow_blocks(struct xfs_inode *ip,
>  		struct xfs_trans **tpp, xfs_fileoff_t offset_fsb,
> -- 
> 2.17.0
> 
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