Commit a8eb4137 authored by Brian Foster's avatar Brian Foster Committed by Carlos Maiolino
Browse files

xfs: look up cow fork extent earlier for buffered iomap_begin 



To further isolate the need for flushing for zero range, we need to
know whether a hole in the data fork is fronted by blocks in the COW
fork or not. COW fork lookup currently occurs further down in the
function, after the zero range case is handled.

As a preparation step, lift the COW fork extent lookup to earlier in
the function, at the same time as the data fork lookup. Only the
lookup logic is lifted. The COW fork branch/reporting logic remains
as is to avoid any observable behavior change from an iomap
reporting perspective.

Signed-off-by: default avatarBrian Foster <bfoster@redhat.com>
Reviewed-by: default avatarDarrick J. Wong <djwong@kernel.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarCarlos Maiolino <cem@kernel.org>
parent c35a3e27

fs/xfs/xfs_iomap.c

+25 −21
Original line number Diff line number Diff line
@@ -1830,14 +1830,29 @@ xfs_buffered_write_iomap_begin( 
		goto out_unlock;



	/*

	 * Search the data fork first to look up our source mapping.  We

	 * always need the data fork map, as we have to return it to the

	 * iomap code so that the higher level write code can read data in to

	 * perform read-modify-write cycles for unaligned writes.

	 * Search the data fork first to look up our source mapping. We always

	 * need the data fork map, as we have to return it to the iomap code so

	 * that the higher level write code can read data in to perform

	 * read-modify-write cycles for unaligned writes.

	 *

	 * Then search the COW fork extent list even if we did not find a data

	 * fork extent. This serves two purposes: first this implements the

	 * speculative preallocation using cowextsize, so that we also unshare

	 * 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.

	 */

	eof = !xfs_iext_lookup_extent(ip, &ip->i_df, offset_fsb, &icur, &imap);

	if (eof)

		imap.br_startoff = end_fsb; /* fake hole until the end */

	if (xfs_is_cow_inode(ip)) {

		if (!ip->i_cowfp) {

			ASSERT(!xfs_is_reflink_inode(ip));

			xfs_ifork_init_cow(ip);

		}

		cow_eof = !xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb,

				&ccur, &cmap);

	}



	/* We never need to allocate blocks for unsharing a hole. */

	if ((flags & IOMAP_UNSHARE) && imap.br_startoff > offset_fsb) {
@@ -1904,25 +1919,14 @@ xfs_buffered_write_iomap_begin( 
	}



	/*

	 * Search the COW fork extent list even if we did not find a data fork

	 * extent.  This serves two purposes: first this implements the

	 * speculative preallocation using cowextsize, so that we also unshare

	 * 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.

	 * Now that we've handled any operation specific special cases, at this

	 * point we can report a COW mapping if found.

	 */

	if (xfs_is_cow_inode(ip)) {

		if (!ip->i_cowfp) {

			ASSERT(!xfs_is_reflink_inode(ip));

			xfs_ifork_init_cow(ip);

		}

		cow_eof = !xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb,

				&ccur, &cmap);

		if (!cow_eof && cmap.br_startoff <= offset_fsb) {

	if (xfs_is_cow_inode(ip) &&

	    !cow_eof && cmap.br_startoff <= offset_fsb) {

		trace_xfs_reflink_cow_found(ip, &cmap);

		goto found_cow;

	}

	}



	if (imap.br_startoff <= offset_fsb) {

		/*