ocfs2: Optionally limit extent size in ocfs2_insert_extent()

In xattr bucket, we want to limit the maximum size of a btree leaf,
otherwise we'll lose the benefits of hashing because we'll have to search
large leaves.

So add a new field in ocfs2_extent_tree which indicates the maximum leaf cluster
size we want so that we can prevent ocfs2_insert_extent() from merging the leaf
record even if it is contiguous with an adjacent record.

Other btree types are not affected by this change.

Signed-off-by: Tao Ma <tao.ma@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>

fs/ocfs2/alloc.h

@@ -32,6 +32,11 @@ enum ocfs2_extent_tree_type {
 	OCFS2_XATTR_TREE_EXTENT,
 };
 
+/*
+ * For xattr tree leaf, we limit the leaf byte size to be 64K.
+ */
+#define OCFS2_MAX_XATTR_TREE_LEAF_SIZE 65536
+
 struct ocfs2_alloc_context;
 int ocfs2_dinode_insert_extent(struct ocfs2_super *osb,
 			       handle_t *handle,