Btrfs: implement memory reclaim for leaf reference cache

The memory reclaiming issue happens when snapshot exists. In that
case, some cache entries may not be used during old snapshot dropping,
so they will remain in the cache until umount.

The patch adds a field to struct btrfs_leaf_ref to record create time. Besides,
the patch makes all dead roots of a given snapshot linked together in order of
create time. After a old snapshot was completely dropped, we check the dead
root list and remove all cache entries created before the oldest dead root in
the list.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index ec1ba8ddb35f..e826730d750f 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -735,8 +735,9 @@ static int __setup_root(u32 nodesize, u32 leafsize, u32 sectorsize,
 
         INIT_LIST_HEAD(&root->dirty_list);
         INIT_LIST_HEAD(&root->orphan_list);
+        INIT_LIST_HEAD(&root->dead_list);
         spin_lock_init(&root->node_lock);
-        spin_lock_init(&root->orphan_lock);
+        spin_lock_init(&root->list_lock);
         mutex_init(&root->objectid_mutex);
 
         btrfs_leaf_ref_tree_init(&root->ref_tree_struct);
@@ -1717,7 +1718,7 @@ int close_ctree(struct btrfs_root *root)
                 printk("btrfs: at umount reference cache size %Lu\n",
                         fs_info->total_ref_cache_size);
         }
-        
+
         if (fs_info->extent_root->node)
                 free_extent_buffer(fs_info->extent_root->node);