Btrfs: cache extent state when writing out dirty metadata pages

Everytime we write out dirty pages we search for an offset in the tree,
convert the bits in the state, and then when we wait we search for the
offset again and clear the bits.  So for every dirty range in the io tree we
are doing 4 rb searches, which is suboptimal.  With this patch we are only
doing 2 searches for every cycle (modulo weird things happening).  Thanks,

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

1 files changed, 9 insertions, 5 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 69139a356f7..77db875b511 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -687,13 +687,15 @@ int btrfs_write_marked_extents(struct btrfs_root *root,
         int err = 0;
         int werr = 0;
         struct address_space *mapping = root->fs_info->btree_inode->i_mapping;
+        struct extent_state *cached_state = NULL;
         u64 start = 0;
         u64 end;
 
         while (!find_first_extent_bit(dirty_pages, start, &start, &end,
-                                      mark)) {
-                convert_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT, mark,
-                                   GFP_NOFS);
+                                      mark, &cached_state)) {
+                convert_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
+                                   mark, &cached_state, GFP_NOFS);
+                cached_state = NULL;
                 err = filemap_fdatawrite_range(mapping, start, end);
                 if (err)
                         werr = err;
@@ -717,12 +719,14 @@ int btrfs_wait_marked_extents(struct btrfs_root *root,
         int err = 0;
         int werr = 0;
         struct address_space *mapping = root->fs_info->btree_inode->i_mapping;
+        struct extent_state *cached_state = NULL;
         u64 start = 0;
         u64 end;
 
         while (!find_first_extent_bit(dirty_pages, start, &start, &end,
-                                      EXTENT_NEED_WAIT)) {
-                clear_extent_bits(dirty_pages, start, end, EXTENT_NEED_WAIT, GFP_NOFS);
+                                      EXTENT_NEED_WAIT, &cached_state)) {
+                clear_extent_bit(dirty_pages, start, end, EXTENT_NEED_WAIT,
+                                 0, 0, &cached_state, GFP_NOFS);
                 err = filemap_fdatawait_range(mapping, start, end);
                 if (err)
                         werr = err;