diff options
| -rw-r--r-- | fs/xfs/libxfs/xfs_bmap.c | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c index aa4bc2b5aab1..f6e44d203786 100644 --- a/fs/xfs/libxfs/xfs_bmap.c +++ b/fs/xfs/libxfs/xfs_bmap.c @@ -6406,6 +6406,28 @@ xfs_get_cowextsz_hint( if (ip->i_diflags2 & XFS_DIFLAG2_COWEXTSIZE) a = ip->i_cowextsize; if (XFS_IS_REALTIME_INODE(ip)) { + /* + * For realtime files, the realtime extent is the fundamental + * unit of allocation. This means that data sharing and CoW + * remapping can only be done in those units. For filesystems + * where the extent size is larger than one block, write + * requests that are not aligned to an extent boundary employ + * an unshare-around strategy to ensure that all pages for a + * shared extent are fully dirtied. + * + * Because the remapping alignment requirement applies equally + * to all CoW writes, any regular overwrites that could be + * turned (by a speculative CoW preallocation) into a CoW write + * must either employ this dirty-around strategy, or be smart + * enough to ignore the CoW fork mapping unless the entire + * extent is dirty or becomes shared by writeback time. Doing + * the first would dramatically increase write amplification, + * and the second would require deeper insight into the state + * of the page cache during a writeback request. For now, we + * ignore the hint. + */ + if (ip->i_mount->m_sb.sb_rextsize > 1) + return ip->i_mount->m_sb.sb_rextsize; b = 0; if (ip->i_diflags & XFS_DIFLAG_EXTSIZE) b = ip->i_extsize; |