Btrfs: optimize read_block_for_search

This patch does two things, first it only does one call to
btrfs_buffer_uptodate() with the gen specified instead of once with 0 and then
again with gen specified.  The other thing is to call btrfs_read_buffer() on the
buffer we've found instead of dropping it and then calling read_tree_block().
This will keep us from doing yet another radix tree lookup for a buffer we've
already found.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/ctree.c

@@ -2359,35 +2359,28 @@ read_block_for_search(struct btrfs_trans_handle *trans,
 	tmp = btrfs_find_tree_block(root, blocknr, blocksize);
 	if (tmp) {
 		/* first we do an atomic uptodate check */
-		if (btrfs_buffer_uptodate(tmp, 0, 1) > 0) {
-			if (btrfs_buffer_uptodate(tmp, gen, 1) > 0) {
-				/*
-				 * we found an up to date block without
-				 * sleeping, return
-				 * right away
-				 */
-				*eb_ret = tmp;
-				return 0;
-			}
-			/* the pages were up to date, but we failed
-			 * the generation number check.  Do a full
-			 * read for the generation number that is correct.
-			 * We must do this without dropping locks so
-			 * we can trust our generation number
-			 */
-			free_extent_buffer(tmp);
-			btrfs_set_path_blocking(p);
+		if (btrfs_buffer_uptodate(tmp, gen, 1) > 0) {
+			*eb_ret = tmp;
+			return 0;
+		}
 
-			/* now we're allowed to do a blocking uptodate check */
-			tmp = read_tree_block(root, blocknr, blocksize, gen);
-			if (tmp && btrfs_buffer_uptodate(tmp, gen, 0) > 0) {
-				*eb_ret = tmp;
-				return 0;
-			}
-			free_extent_buffer(tmp);
-			btrfs_release_path(p);
-			return -EIO;
+		/* the pages were up to date, but we failed
+		 * the generation number check.  Do a full
+		 * read for the generation number that is correct.
+		 * We must do this without dropping locks so
+		 * we can trust our generation number
+		 */
+		btrfs_set_path_blocking(p);
+
+		/* now we're allowed to do a blocking uptodate check */
+		ret = btrfs_read_buffer(tmp, gen);
+		if (!ret) {
+			*eb_ret = tmp;
+			return 0;
 		}
+		free_extent_buffer(tmp);
+		btrfs_release_path(p);
+		return -EIO;
 	}
 
 	/*