Btrfs: prepare block group cache before writing

Writing the block group cache will modify the extent tree quite a bit because it
truncates the old space cache and pre-allocates new stuff.  To try and cut down
on the churn lets do the setup dance first, then later on hopefully we can avoid
looping with newly dirtied roots.  Thanks,

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

1 files changed, 26 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 96c613bfe157..3ac3fefb1625 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3325,6 +3325,32 @@ out:
 	return ret;
 }
 
+int btrfs_setup_space_cache(struct btrfs_trans_handle *trans,
+			    struct btrfs_root *root)
+{
+	struct btrfs_block_group_cache *cache, *tmp;
+	struct btrfs_transaction *cur_trans = trans->transaction;
+	struct btrfs_path *path;
+
+	if (list_empty(&cur_trans->dirty_bgs) ||
+	    !btrfs_test_opt(root, SPACE_CACHE))
+		return 0;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	/* Could add new block groups, use _safe just in case */
+	list_for_each_entry_safe(cache, tmp, &cur_trans->dirty_bgs,
+				 dirty_list) {
+		if (cache->disk_cache_state == BTRFS_DC_CLEAR)
+			cache_save_setup(cache, trans, path);
+	}
+
+	btrfs_free_path(path);
+	return 0;
+}
+
 int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans,
 				   struct btrfs_root *root)
 {