Merge branch 'for-linus' of git://oss.sgi.com:8090/xfs/xfs-pull

* 'for-linus' of git://oss.sgi.com:8090/xfs/xfs-pull: (64 commits)
  [XFS] Remove vn_revalidate calls in xfs.
  [XFS] Now that xfs_setattr is only used for attributes set from ->setattr
  [XFS] xfs_setattr currently doesn't just handle the attributes set through
  [XFS] fix use after free with external logs or real-time devices
  [XFS] A bug was found in xfs_bmap_add_extent_unwritten_real(). In a
  [XFS] fix compilation without CONFIG_PROC_FS
  [XFS] s/XFS_PURGE_INODE/IRELE/g s/VN_HOLD(XFS_ITOV())/IHOLD()/
  [XFS] fix mount option parsing in remount
  [XFS] Disable queue flag test in barrier check.
  [XFS] streamline init/exit path
  [XFS] Fix up problem when CONFIG_XFS_POSIX_ACL is not set and yet we still
  [XFS] Don't assert if trying to mount with blocksize > pagesize
  [XFS] Don't update mtime on rename source
  [XFS] Allow xfs_bmbt_split() to fallback to the lowspace allocator
  [XFS] Restore the lowspace extent allocator algorithm
  [XFS] use minleft when allocating in xfs_bmbt_split()
  [XFS] attrmulti cleanup
  [XFS] Check for invalid flags in xfs_attrlist_by_handle.
  [XFS] Fix CI lookup in leaf-form directories
  [XFS] Use the generic xattr methods.
  ...

1 files changed, 12 insertions, 1 deletions

diff --git a/fs/xfs/xfs_bmap.h b/fs/xfs/xfs_bmap.h
index 6ff70cda451..9f3e3a836d1 100644
--- a/fs/xfs/xfs_bmap.h
+++ b/fs/xfs/xfs_bmap.h
@@ -54,12 +54,23 @@ typedef struct xfs_bmap_free_item
 
 /*
  * Header for free extent list.
+ *
+ * xbf_low is used by the allocator to activate the lowspace algorithm -
+ * when free space is running low the extent allocator may choose to
+ * allocate an extent from an AG without leaving sufficient space for
+ * a btree split when inserting the new extent.  In this case the allocator
+ * will enable the lowspace algorithm which is supposed to allow further
+ * allocations (such as btree splits and newroots) to allocate from
+ * sequential AGs.  In order to avoid locking AGs out of order the lowspace
+ * algorithm will start searching for free space from AG 0.  If the correct
+ * transaction reservations have been made then this algorithm will eventually
+ * find all the space it needs.
  */
 typedef	struct xfs_bmap_free
 {
 	xfs_bmap_free_item_t	*xbf_first;	/* list of to-be-free extents */
 	int			xbf_count;	/* count of items on list */
-	int			xbf_low;	/* kludge: alloc in low mode */
+	int			xbf_low;	/* alloc in low mode */
 } xfs_bmap_free_t;
 
 #define	XFS_BMAP_MAX_NMAP	4