xfs: optimize writes to reflink files

Instead of reserving space as the first thing in write_begin move it past
reading the extent in the data fork.  That way we only have to read from
the data fork once and can reuse that information for trimming the extent
to the shared/unshared boundary.  Additionally this allows to easily
limit the actual write size to said boundary, and avoid a roundtrip on the
ilock.

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>

1 files changed, 58 insertions, 84 deletions

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 6c4c215634ec..9c477de3c1ac 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -228,50 +228,54 @@ xfs_reflink_trim_around_shared(
 	}
 }
 
-/* Create a CoW reservation for a range of blocks within a file. */
-static int
-__xfs_reflink_reserve_cow(
+/*
+ * Trim the passed in imap to the next shared/unshared extent boundary, and
+ * if imap->br_startoff points to a shared extent reserve space for it in the
+ * COW fork.  In this case *shared is set to true, else to false.
+ *
+ * Note that imap will always contain the block numbers for the existing blocks
+ * in the data fork, as the upper layers need them for read-modify-write
+ * operations.
+ */
+int
+xfs_reflink_reserve_cow(
 	struct xfs_inode	*ip,
-	xfs_fileoff_t		*offset_fsb,
-	xfs_fileoff_t		end_fsb,
-	bool			*skipped)
+	struct xfs_bmbt_irec	*imap,
+	bool			*shared)
 {
-	struct xfs_bmbt_irec	got, prev, imap;
-	xfs_fileoff_t		orig_end_fsb;
-	int			nimaps, eof = 0, error = 0;
-	bool			shared = false, trimmed = false;
+	struct xfs_bmbt_irec	got, prev;
+	xfs_fileoff_t		end_fsb, orig_end_fsb;
+	int			eof = 0, error = 0;
+	bool			trimmed;
 	xfs_extnum_t		idx;
 	xfs_extlen_t		align;
 
-	/* Already reserved?  Skip the refcount btree access. */
-	xfs_bmap_search_extents(ip, *offset_fsb, XFS_COW_FORK, &eof, &idx,
+	/*
+	 * Search the COW fork extent list first.  This serves two purposes:
+	 * first this implement the speculative preallocation using cowextisze,
+	 * so that we also unshared block adjacent to shared blocks instead
+	 * of just the shared blocks themselves.  Second the lookup in the
+	 * extent list is generally faster than going out to the shared extent
+	 * tree.
+	 */
+	xfs_bmap_search_extents(ip, imap->br_startoff, XFS_COW_FORK, &eof, &idx,
 			&got, &prev);
-	if (!eof && got.br_startoff <= *offset_fsb) {
-		end_fsb = orig_end_fsb = got.br_startoff + got.br_blockcount;
-		trace_xfs_reflink_cow_found(ip, &got);
-		goto done;
-	}
+	if (!eof && got.br_startoff <= imap->br_startoff) {
+		trace_xfs_reflink_cow_found(ip, imap);
+		xfs_trim_extent(imap, got.br_startoff, got.br_blockcount);
 
-	/* Read extent from the source file. */
-	nimaps = 1;
-	error = xfs_bmapi_read(ip, *offset_fsb, end_fsb - *offset_fsb,
-			&imap, &nimaps, 0);
-	if (error)
-		goto out_unlock;
-	ASSERT(nimaps == 1);
+		*shared = true;
+		return 0;
+	}
 
 	/* Trim the mapping to the nearest shared extent boundary. */
-	error = xfs_reflink_trim_around_shared(ip, &imap, &shared, &trimmed);
+	error = xfs_reflink_trim_around_shared(ip, imap, shared, &trimmed);
 	if (error)
-		goto out_unlock;
-
-	end_fsb = orig_end_fsb = imap.br_startoff + imap.br_blockcount;
+		return error;
 
 	/* Not shared?  Just report the (potentially capped) extent. */
-	if (!shared) {
-		*skipped = true;
-		goto done;
-	}
+	if (!*shared)
+		return 0;
 
 	/*
 	 * Fork all the shared blocks from our write offset until the end of
@@ -279,72 +283,38 @@ __xfs_reflink_reserve_cow(
 	 */
 	error = xfs_qm_dqattach_locked(ip, 0);
 	if (error)
-		goto out_unlock;
+		return error;
+
+	end_fsb = orig_end_fsb = imap->br_startoff + imap->br_blockcount;
 
 	align = xfs_eof_alignment(ip, xfs_get_cowextsz_hint(ip));
 	if (align)
 		end_fsb = roundup_64(end_fsb, align);
 
 retry:
-	error = xfs_bmapi_reserve_delalloc(ip, XFS_COW_FORK, *offset_fsb,
-			end_fsb - *offset_fsb, &got,
-			&prev, &idx, eof);
+	error = xfs_bmapi_reserve_delalloc(ip, XFS_COW_FORK, imap->br_startoff,
+			end_fsb - imap->br_startoff, &got, &prev, &idx, eof);
 	switch (error) {
 	case 0:
 		break;
 	case -ENOSPC:
 	case -EDQUOT:
 		/* retry without any preallocation */
-		trace_xfs_reflink_cow_enospc(ip, &imap);
+		trace_xfs_reflink_cow_enospc(ip, imap);
 		if (end_fsb != orig_end_fsb) {
 			end_fsb = orig_end_fsb;
 			goto retry;
 		}
 		/*FALLTHRU*/
 	default:
-		goto out_unlock;
+		return error;
 	}
 
 	if (end_fsb != orig_end_fsb)
 		xfs_inode_set_cowblocks_tag(ip);
 
 	trace_xfs_reflink_cow_alloc(ip, &got);
-done:
-	*offset_fsb = end_fsb;
-out_unlock:
-	return error;
-}
-
-/* Create a CoW reservation for part of a file. */
-int
-xfs_reflink_reserve_cow_range(
-	struct xfs_inode	*ip,
-	xfs_off_t		offset,
-	xfs_off_t		count)
-{
-	struct xfs_mount	*mp = ip->i_mount;
-	xfs_fileoff_t		offset_fsb, end_fsb;
-	bool			skipped = false;
-	int			error = 0;
-
-	trace_xfs_reflink_reserve_cow_range(ip, offset, count);
-
-	offset_fsb = XFS_B_TO_FSBT(mp, offset);
-	end_fsb = XFS_B_TO_FSB(mp, offset + count);
-
-	xfs_ilock(ip, XFS_ILOCK_EXCL);
-	while (offset_fsb < end_fsb) {
-		error = __xfs_reflink_reserve_cow(ip, &offset_fsb, end_fsb,
-				&skipped);
-		if (error) {
-			trace_xfs_reflink_reserve_cow_range_error(ip, error,
-				_RET_IP_);
-			break;
-		}
-	}
-	xfs_iunlock(ip, XFS_ILOCK_EXCL);
-
-	return error;
+	return 0;
 }
 
 /* Allocate all CoW reservations covering a range of blocks in a file. */
@@ -359,9 +329,8 @@ __xfs_reflink_allocate_cow(
 	struct xfs_defer_ops	dfops;
 	struct xfs_trans	*tp;
 	xfs_fsblock_t		first_block;
-	xfs_fileoff_t		next_fsb;
 	int			nimaps = 1, error;
-	bool			skipped = false;
+	bool			shared;
 
 	xfs_defer_init(&dfops, &first_block);
 
@@ -372,33 +341,38 @@ __xfs_reflink_allocate_cow(
 
 	xfs_ilock(ip, XFS_ILOCK_EXCL);
 
-	next_fsb = *offset_fsb;
-	error = __xfs_reflink_reserve_cow(ip, &next_fsb, end_fsb, &skipped);
+	/* Read extent from the source file. */
+	nimaps = 1;
+	error = xfs_bmapi_read(ip, *offset_fsb, end_fsb - *offset_fsb,
+			&imap, &nimaps, 0);
+	if (error)
+		goto out_unlock;
+	ASSERT(nimaps == 1);
+
+	error = xfs_reflink_reserve_cow(ip, &imap, &shared);
 	if (error)
 		goto out_trans_cancel;
 
-	if (skipped) {
-		*offset_fsb = next_fsb;
+	if (!shared) {
+		*offset_fsb = imap.br_startoff + imap.br_blockcount;
 		goto out_trans_cancel;
 	}
 
 	xfs_trans_ijoin(tp, ip, 0);
-	error = xfs_bmapi_write(tp, ip, *offset_fsb, next_fsb - *offset_fsb,
+	error = xfs_bmapi_write(tp, ip, imap.br_startoff, imap.br_blockcount,
 			XFS_BMAPI_COWFORK, &first_block,
 			XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK),
 			&imap, &nimaps, &dfops);
 	if (error)
 		goto out_trans_cancel;
 
-	/* We might not have been able to map the whole delalloc extent */
-	*offset_fsb = min(*offset_fsb + imap.br_blockcount, next_fsb);
-
 	error = xfs_defer_finish(&tp, &dfops, NULL);
 	if (error)
 		goto out_trans_cancel;
 
 	error = xfs_trans_commit(tp);
 
+	*offset_fsb = imap.br_startoff + imap.br_blockcount;
 out_unlock:
 	xfs_iunlock(ip, XFS_ILOCK_EXCL);
 	return error;