[PATCH] ext4: try fast merge operation in ext4_mb_free_metadata()

[jing zhang <zj.barak@gmail.com>]

From: Jing Zhang <zj.barak@gmail.com>

Date: Wed Mar 24 21:30:22     2010

There may exist fast path for merge if merge-able.

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Andreas Dilger <adilger@sun.com>
Cc: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Signed-off-by: Jing Zhang <zj.barak@gmail.com>

---

--- linux-2.6.32/fs/ext4/mballoc.c	2009-12-03 11:51:22.000000000 +0800
+++ ext4_mm_leak/mballoc7.c	2010-03-24 21:27:24.000000000 +0800
@@ -4385,6 +4385,24 @@ ext4_mb_free_metadata(handle_t *handle,
 		}
 	}

+	if (parent) {
+		/* let's try fast path */
+		entry = rb_entry(parent, struct ext4_free_data, node);
+		if (n == &parent->rb_left) {
+			if (can_merge(new_entry, entry)) {
+				entry->start_blk = new_entry->start_blk;
+				entry->count += new_entry->count;
+				/* and info the caller that new_entry is
+				 * not used yet.
+				 */
+				return 0;
+			}
+		}
+		else if (can_merge(entry, new_entry)) {
+			entry->count += new_entry->count;
+			return 0;
+		}
+	}
 	rb_link_node(new_node, parent, n);
 	rb_insert_color(new_node, &db->bb_free_root);