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>

1 files changed, 20 insertions, 27 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 1c9dc71089ce..c85cde761248 100644
--- a/fs/btrfs/ctree.c
+++ b/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;
         }
 
         /*