xfs: speed up free inode search

Don't search too far - abort if it is outside a certain radius and simply do
a linear search for the first free inode.  In AGs with a million inodes this
can speed up allocation speed by 3-4x.

[hch: ported to the new xfs_ialloc.c world order]

Signed-off-by: Dave Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Felix Blyakher <felixb@sgi.com>
diff --git a/fs/xfs/xfs_ag.h b/fs/xfs/xfs_ag.h
index f24b50b..a5d54bf 100644
--- a/fs/xfs/xfs_ag.h
+++ b/fs/xfs/xfs_ag.h
@@ -198,6 +198,15 @@
 	xfs_agino_t	pagi_count;	/* number of allocated inodes */
 	int		pagb_count;	/* pagb slots in use */
 	xfs_perag_busy_t *pagb_list;	/* unstable blocks */
+
+	/*
+	 * Inode allocation search lookup optimisation.
+	 * If the pagino matches, the search for new inodes
+	 * doesn't need to search the near ones again straight away
+	 */
+	xfs_agino_t	pagl_pagino;
+	xfs_agino_t	pagl_leftrec;
+	xfs_agino_t	pagl_rightrec;
 #ifdef __KERNEL__
 	spinlock_t	pagb_lock;	/* lock for pagb_list */