xfs: remove i_iolock and use i_rwsem in the VFS inode instead

This patch drops the XFS-own i_iolock and uses the VFS i_rwsem which
recently replaced i_mutex instead.  This means we only have to take
one lock instead of two in many fast path operations, and we can
also shrink the xfs_inode structure.  Thanks to the xfs_ilock family
there is very little churn, the only thing of note is that we need
to switch to use the lock_two_directory helper for taking the i_rwsem
on two inodes in a few places to make sure our lock order matches
the one used in the VFS.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 2 insertions, 5 deletions

diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index 71e8a81c91a3..10dcf27b4c85 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -56,7 +56,6 @@ typedef struct xfs_inode {
         /* Transaction and locking information. */
         struct xfs_inode_log_item *i_itemp;     /* logging information */
         mrlock_t                i_lock;         /* inode lock */
-        mrlock_t                i_iolock;       /* inode IO lock */
         mrlock_t                i_mmaplock;     /* inode mmap IO lock */
         atomic_t                i_pincount;     /* inode pin count */
         spinlock_t              i_flags_lock;   /* inode i_flags lock */
@@ -333,7 +332,7 @@ static inline void xfs_ifunlock(struct xfs_inode *ip)
  * IOLOCK values
  *
  * 0-3          subclass value
- * 4-7          PARENT subclass values
+ * 4-7          unused
  *
  * MMAPLOCK values
  *
@@ -348,10 +347,8 @@ static inline void xfs_ifunlock(struct xfs_inode *ip)
  * 
  */
 #define XFS_IOLOCK_SHIFT                16
-#define XFS_IOLOCK_PARENT_VAL           4
-#define XFS_IOLOCK_MAX_SUBCLASS         (XFS_IOLOCK_PARENT_VAL - 1)
+#define XFS_IOLOCK_MAX_SUBCLASS         3
 #define XFS_IOLOCK_DEP_MASK             0x000f0000
-#define XFS_IOLOCK_PARENT               (XFS_IOLOCK_PARENT_VAL << XFS_IOLOCK_SHIFT)
 
 #define XFS_MMAPLOCK_SHIFT              20
 #define XFS_MMAPLOCK_NUMORDER           0