xfs: factor out code to find the longest free extent in the AG

Signed-off-by: Dave Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
index 028e44e..2cf944e 100644
--- a/fs/xfs/xfs_alloc.c
+++ b/fs/xfs/xfs_alloc.c
@@ -1872,6 +1872,25 @@
 }
 
 /*
+ * Find the length of the longest extent in an AG.
+ */
+xfs_extlen_t
+xfs_alloc_longest_free_extent(
+	struct xfs_mount	*mp,
+	struct xfs_perag	*pag)
+{
+	xfs_extlen_t		need, delta = 0;
+
+	need = XFS_MIN_FREELIST_PAG(pag, mp);
+	if (need > pag->pagf_flcount)
+		delta = need - pag->pagf_flcount;
+
+	if (pag->pagf_longest > delta)
+		return pag->pagf_longest - delta;
+	return pag->pagf_flcount > 0 || pag->pagf_longest > 0;
+}
+
+/*
  * Decide whether to use this allocation group for this allocation.
  * If so, fix up the btree freelist's size.
  */
@@ -1923,15 +1942,12 @@
 	}
 
 	if (!(flags & XFS_ALLOC_FLAG_FREEING)) {
-		need = XFS_MIN_FREELIST_PAG(pag, mp);
-		delta = need > pag->pagf_flcount ? need - pag->pagf_flcount : 0;
 		/*
 		 * If it looks like there isn't a long enough extent, or enough
 		 * total blocks, reject it.
 		 */
-		longest = (pag->pagf_longest > delta) ?
-			(pag->pagf_longest - delta) :
-			(pag->pagf_flcount > 0 || pag->pagf_longest > 0);
+		need = XFS_MIN_FREELIST_PAG(pag, mp);
+		longest = xfs_alloc_longest_free_extent(mp, pag);
 		if ((args->minlen + args->alignment + args->minalignslop - 1) >
 				longest ||
 		    ((int)(pag->pagf_freeblks + pag->pagf_flcount -