xfs: optimize xfs_reflink_cancel_cow_blocks

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>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_reflink.c

@@ -511,53 +511,49 @@ 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);
+	while (got.br_startoff < end_fsb) {
+		del = got;
+		xfs_trim_extent(&del, offset_fsb, end_fsb - offset_fsb);
+		trace_xfs_reflink_cancel_cow(ip, &del);
 
-		if (irec.br_startblock == DELAYSTARTBLOCK) {
-			/* 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);
@@ -567,13 +563,12 @@ 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);
 	}
 
 	return error;