Re: [PATCH 7/9] xfs: optimize xfs_reflink_cancel_cow_blocks

[Brian Foster <bfoster@redhat.com>]

On Mon, Oct 10, 2016 at 03:38:03PM +0200, Christoph Hellwig wrote:
> Rewrite xfs_reflink_cancel_cow_blocks so that we only do a search for
> the first extent in the extent list and then iterate over the remaining
> extents using the extent index, passing the extent we operate on
> directly to xfs_bmap_del_extent_delay or xfs_bmap_del_extent_cow instead
> of going through xfs_bunmapi and doing yet another extent list lookup.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/xfs_reflink.c | 59 +++++++++++++++++++++++-----------------------------
>  1 file changed, 26 insertions(+), 33 deletions(-)
> 
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 5d230ea..08170bb 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -512,58 +512,52 @@ xfs_reflink_cancel_cow_blocks(
>  	xfs_fileoff_t			offset_fsb,
>  	xfs_fileoff_t			end_fsb)
>  {
> -	struct xfs_bmbt_irec		irec;
> -	xfs_filblks_t			count_fsb;
> +	struct xfs_ifork		*ifp = XFS_IFORK_PTR(ip, XFS_COW_FORK);
> +	struct xfs_bmbt_irec		got, prev, del;
> +	xfs_extnum_t			idx;
>  	xfs_fsblock_t			firstfsb;
>  	struct xfs_defer_ops		dfops;
> -	int				error = 0;
> -	int				nimaps;
> +	int				error = 0, eof = 0;
>  
>  	if (!xfs_is_reflink_inode(ip))
>  		return 0;
>  
> -	/* Go find the old extent in the CoW fork. */
> -	while (offset_fsb < end_fsb) {
> -		nimaps = 1;
> -		count_fsb = (xfs_filblks_t)(end_fsb - offset_fsb);
> -		error = xfs_bmapi_read(ip, offset_fsb, count_fsb, &irec,
> -				&nimaps, XFS_BMAPI_COWFORK);
> -		if (error)
> -			break;
> -		ASSERT(nimaps == 1);
> +	xfs_bmap_search_extents(ip, offset_fsb, XFS_COW_FORK, &eof, &idx,
> +			&got, &prev);
> +	if (eof)
> +		return 0;
>  
> -		trace_xfs_reflink_cancel_cow(ip, &irec);
> +	do {
> +		if (got.br_startoff >= end_fsb)
> +			break;

How about using a while loop..?

	while (got.br_startoff < end_fsb) {
		...

Otherwise, looks fine:

Reviewed-by: Brian Foster <bfoster@redhat.com>

>  
> -		if (irec.br_startblock == DELAYSTARTBLOCK) {
> -			/* Free a delayed allocation. */
> -			xfs_mod_fdblocks(ip->i_mount, irec.br_blockcount,
> -					false);
> -			ip->i_delayed_blks -= irec.br_blockcount;
> +		del = got;
> +		xfs_trim_extent(&del, offset_fsb, end_fsb - offset_fsb);
> +		trace_xfs_reflink_cancel_cow(ip, &del);
>  
> -			/* Remove the mapping from the CoW fork. */
> -			error = xfs_bunmapi_cow(ip, &irec);
> +		if (isnullstartblock(del.br_startblock)) {
> +			error = xfs_bmap_del_extent_delay(ip, XFS_COW_FORK,
> +					&idx, &got, &del);
>  			if (error)
>  				break;
> -		} else if (irec.br_startblock == HOLESTARTBLOCK) {
> -			/* empty */
>  		} else {
>  			xfs_trans_ijoin(*tpp, ip, 0);
>  			xfs_defer_init(&dfops, &firstfsb);
>  
>  			/* Free the CoW orphan record. */
>  			error = xfs_refcount_free_cow_extent(ip->i_mount,
> -					&dfops, irec.br_startblock,
> -					irec.br_blockcount);
> +					&dfops, del.br_startblock,
> +					del.br_blockcount);
>  			if (error)
>  				break;
>  
>  			xfs_bmap_add_free(ip->i_mount, &dfops,
> -					irec.br_startblock, irec.br_blockcount,
> +					del.br_startblock, del.br_blockcount,
>  					NULL);
>  
>  			/* Update quota accounting */
>  			xfs_trans_mod_dquot_byino(*tpp, ip, XFS_TRANS_DQ_BCOUNT,
> -					-(long)irec.br_blockcount);
> +					-(long)del.br_blockcount);
>  
>  			/* Roll the transaction */
>  			error = xfs_defer_finish(tpp, &dfops, ip);
> @@ -573,14 +567,13 @@ xfs_reflink_cancel_cow_blocks(
>  			}
>  
>  			/* Remove the mapping from the CoW fork. */
> -			error = xfs_bunmapi_cow(ip, &irec);
> -			if (error)
> -				break;
> +			xfs_bmap_del_extent_cow(ip, &idx, &got, &del);
>  		}
>  
> -		/* Roll on... */
> -		offset_fsb = irec.br_startoff + irec.br_blockcount;
> -	}
> +		if (++idx >= ifp->if_bytes / sizeof(struct xfs_bmbt_rec))
> +			return 0;
> +		xfs_bmbt_get_all(xfs_iext_get_ext(ifp, idx), &got);
> +	} while (1);
>  
>  	return error;
>  }
> -- 
> 2.10.1.382.ga23ca1b
> 
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