1 files changed, 21 insertions, 3 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 67bd12a52369..3ca26d84cce5 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2903,8 +2903,13 @@ again:
         }
 
         spin_lock(&block_group->lock);
-        if (block_group->cached != BTRFS_CACHE_FINISHED) {
-                /* We're not cached, don't bother trying to write stuff out */
+        if (block_group->cached != BTRFS_CACHE_FINISHED ||
+            !btrfs_test_opt(root, SPACE_CACHE)) {
+                /*
+                 * don't bother trying to write stuff out _if_
+                 * a) we're not cached,
+                 * b) we're with nospace_cache mount option.
+                 */
                 dcs = BTRFS_DC_WRITTEN;
                 spin_unlock(&block_group->lock);
                 goto out_put;
@@ -7614,8 +7619,21 @@ int btrfs_read_block_groups(struct btrfs_root *root)
                 INIT_LIST_HEAD(&cache->list);
                 INIT_LIST_HEAD(&cache->cluster_list);
 
-                if (need_clear)
+                if (need_clear) {
+                        /*
+                         * When we mount with old space cache, we need to
+                         * set BTRFS_DC_CLEAR and set dirty flag.
+                         *
+                         * a) Setting 'BTRFS_DC_CLEAR' makes sure that we
+                         *    truncate the old free space cache inode and
+                         *    setup a new one.
+                         * b) Setting 'dirty flag' makes sure that we flush
+                         *    the new space cache info onto disk.
+                         */
                         cache->disk_cache_state = BTRFS_DC_CLEAR;
+                        if (btrfs_test_opt(root, SPACE_CACHE))
+                                cache->dirty = 1;
+                }
 
                 read_extent_buffer(leaf, &cache->item,
                                    btrfs_item_ptr_offset(leaf, path->slots[0]),