Commit c770f997 authored by Brian Foster's avatar Brian Foster Committed by Carlos Maiolino
Browse files

xfs: only flush when COW fork blocks overlap data fork holes 



The zero range hole mapping flush case has been lifted from iomap
into XFS. Now that we have more mapping context available from the
->iomap_begin() handler, we can isolate the flush further to when we
know a hole is fronted by COW blocks.

Rather than purely rely on pagecache dirty state, explicitly check
for the case where a range is a hole in both forks. Otherwise trim
to the range where there does happen to be overlap and use that for
the pagecache writeback check. This might prevent some spurious
zeroing, but more importantly makes it easier to remove the flush
entirely.

Signed-off-by: default avatarBrian Foster <bfoster@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDarrick J. Wong <djwong@kernel.org>
Signed-off-by: default avatarCarlos Maiolino <cem@kernel.org>
parent a8eb4137

fs/xfs/xfs_iomap.c

+30 −6
Original line number Diff line number Diff line
@@ -1781,10 +1781,12 @@ xfs_buffered_write_iomap_begin( 
{

	struct iomap_iter	*iter = container_of(iomap, struct iomap_iter,

						     iomap);

	struct address_space	*mapping = inode->i_mapping;

	struct xfs_inode	*ip = XFS_I(inode);

	struct xfs_mount	*mp = ip->i_mount;

	xfs_fileoff_t		offset_fsb = XFS_B_TO_FSBT(mp, offset);

	xfs_fileoff_t		end_fsb = xfs_iomap_end_fsb(mp, offset, count);

	xfs_fileoff_t		cow_fsb = NULLFILEOFF;

	struct xfs_bmbt_irec	imap, cmap;

	struct xfs_iext_cursor	icur, ccur;

	xfs_fsblock_t		prealloc_blocks = 0;
@@ -1852,6 +1854,8 @@ xfs_buffered_write_iomap_begin( 
		}

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

				&ccur, &cmap);

		if (!cow_eof)

			cow_fsb = cmap.br_startoff;

	}



	/* We never need to allocate blocks for unsharing a hole. */
@@ -1866,17 +1870,37 @@ xfs_buffered_write_iomap_begin( 
	 * writeback to remap pending blocks and restart the lookup.

	 */

	if ((flags & IOMAP_ZERO) && imap.br_startoff > offset_fsb) {

		if (filemap_range_needs_writeback(inode->i_mapping, offset,

				offset + count - 1)) {

		loff_t	start, end;



		imap.br_blockcount = imap.br_startoff - offset_fsb;

		imap.br_startoff = offset_fsb;

		imap.br_startblock = HOLESTARTBLOCK;

		imap.br_state = XFS_EXT_NORM;



		if (cow_fsb == NULLFILEOFF)

			goto found_imap;

		if (cow_fsb > offset_fsb) {

			xfs_trim_extent(&imap, offset_fsb,

					cow_fsb - offset_fsb);

			goto found_imap;

		}



		/* COW fork blocks overlap the hole */

		xfs_trim_extent(&imap, offset_fsb,

			    cmap.br_startoff + cmap.br_blockcount - offset_fsb);

		start = XFS_FSB_TO_B(mp, imap.br_startoff);

		end = XFS_FSB_TO_B(mp,

				   imap.br_startoff + imap.br_blockcount) - 1;

		if (filemap_range_needs_writeback(mapping, start, end)) {

			xfs_iunlock(ip, lockmode);

			error = filemap_write_and_wait_range(inode->i_mapping,

					offset, offset + count - 1);

			error = filemap_write_and_wait_range(mapping, start,

							     end);

			if (error)

				return error;

			goto restart;

		}

		xfs_hole_to_iomap(ip, iomap, offset_fsb, imap.br_startoff);

		goto out_unlock;



		goto found_imap;

	}



	/*