xfs: replace i_pin_wait with a bit waitqueue

Replace i_pin_wait, which is only used during synchronous inode flushing
with a bit waitqueue.  This trades off a much smaller inode against
slightly slower wakeup performance, and saves 12 (32-bit) or 20 (64-bit)
bytes in the XFS inode.
Reviewed-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_inode.c

@@ -2037,7 +2037,7 @@ xfs_idestroy_fork(
  * once someone is waiting for it to be unpinned.
  */
 static void
-xfs_iunpin_nowait(
+xfs_iunpin(
 	struct xfs_inode	*ip)
 {
 	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL|XFS_ILOCK_SHARED));
@@ -2049,14 +2049,29 @@ xfs_iunpin_nowait(
 
 }
 
+static void
+__xfs_iunpin_wait(
+	struct xfs_inode	*ip)
+{
+	wait_queue_head_t *wq = bit_waitqueue(&ip->i_flags, __XFS_IPINNED_BIT);
+	DEFINE_WAIT_BIT(wait, &ip->i_flags, __XFS_IPINNED_BIT);
+
+	xfs_iunpin(ip);
+
+	do {
+		prepare_to_wait(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
+		if (xfs_ipincount(ip))
+			io_schedule();
+	} while (xfs_ipincount(ip));
+	finish_wait(wq, &wait.wait);
+}
+
 void
 xfs_iunpin_wait(
 	struct xfs_inode	*ip)
 {
-	if (xfs_ipincount(ip)) {
-		xfs_iunpin_nowait(ip);
-		wait_event(ip->i_ipin_wait, (xfs_ipincount(ip) == 0));
-	}
+	if (xfs_ipincount(ip))
+		__xfs_iunpin_wait(ip);
 }
 
 /*
@@ -2415,7 +2430,7 @@ xfs_iflush(
 	 * out for us if they occur after the log force completes.
 	 */
 	if (!(flags & SYNC_WAIT) && xfs_ipincount(ip)) {
-		xfs_iunpin_nowait(ip);
+		xfs_iunpin(ip);
 		xfs_ifunlock(ip);
 		return EAGAIN;
 	}

fs/xfs/xfs_inode.h

@@ -238,7 +238,6 @@ typedef struct xfs_inode {
 	mrlock_t		i_lock;		/* inode lock */
 	mrlock_t		i_iolock;	/* inode IO lock */
 	atomic_t		i_pincount;	/* inode pin count */
-	wait_queue_head_t	i_ipin_wait;	/* inode pinning wait queue */
 	spinlock_t		i_flags_lock;	/* inode i_flags lock */
 	/* Miscellaneous state. */
 	unsigned long		i_flags;	/* see defined flags below */
@@ -367,6 +366,8 @@ xfs_set_projid(struct xfs_inode *ip,
 #define XFS_IDIRTY_RELEASE	(1 << 6) /* dirty release already seen */
 #define __XFS_IFLOCK_BIT	7	 /* inode is being flushed right now */
 #define XFS_IFLOCK		(1 << __XFS_IFLOCK_BIT)
+#define __XFS_IPINNED_BIT	8	 /* wakeup key for zero pin count */
+#define XFS_IPINNED		(1 << __XFS_IPINNED_BIT)
 
 /*
  * Per-lifetime flags need to be reset when re-using a reclaimable inode during

fs/xfs/xfs_inode_item.c

@@ -555,7 +555,7 @@ xfs_inode_item_unpin(
 	trace_xfs_inode_unpin(ip, _RET_IP_);
 	ASSERT(atomic_read(&ip->i_pincount) > 0);
 	if (atomic_dec_and_test(&ip->i_pincount))
-		wake_up(&ip->i_ipin_wait);
+		wake_up_bit(&ip->i_flags, __XFS_IPINNED_BIT);
 }
 
 /*

fs/xfs/xfs_super.c

@@ -828,7 +828,6 @@ xfs_fs_inode_init_once(
 	/* xfs inode */
 	atomic_set(&ip->i_pincount, 0);
 	spin_lock_init(&ip->i_flags_lock);
-	init_waitqueue_head(&ip->i_ipin_wait);
 
 	mrlock_init(&ip->i_lock, MRLOCK_ALLOW_EQUAL_PRI|MRLOCK_BARRIER,
 		     "xfsino", ip->i_ino);