Btrfs: change how we unpin extents

We are racy with async block caching and unpinning extents.  This patch makes
things much less complicated by only unpinning the extent if the block group is
cached.  We check the block_group->cached var under the block_group->lock spin
lock.  If it is set to BTRFS_CACHE_FINISHED then we update the pinned counters,
and unpin the extent and add the free space back.  If it is not set to this, we
start the caching of the block group so the next time we unpin extents we can
unpin the extent.  This keeps us from racing with the async caching threads,
lets us kill the fs wide async thread counter, and keeps us from having to set
DELALLOC bits for every extent we hit if there are caching kthreads going.

One thing that needed to be changed was btrfs_free_super_mirror_extents.  Now
instead of just looking for LOCKED extents, we also look for DIRTY extents,
since we could have left some extents pinned in the previous transaction that
will never get freed now that we are unmounting, which would cause us to leak
memory.  So btrfs_free_super_mirror_extents has been changed to
btrfs_free_pinned_extents, and it will clear the extents locked for the super
mirror, and any remaining pinned extents that may be present.  Thank you,

Signed-off-by: Josef Bacik <jbacik@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 42b03c4ee494..17ad92c29cfd 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -845,7 +845,6 @@ struct btrfs_fs_info {
         atomic_t async_submit_draining;
         atomic_t nr_async_bios;
         atomic_t async_delalloc_pages;
-        atomic_t async_caching_threads;
 
         /*
          * this is used by the balancing code to wait for all the pending
@@ -1926,7 +1925,7 @@ int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
                            struct btrfs_root *root, unsigned long count);
 int btrfs_lookup_extent(struct btrfs_root *root, u64 start, u64 len);
 int btrfs_update_pinned_extents(struct btrfs_root *root,
-                                u64 bytenr, u64 num, int pin, int mark_free);
+                                u64 bytenr, u64 num, int pin);
 int btrfs_drop_leaf_ref(struct btrfs_trans_handle *trans,
                         struct btrfs_root *root, struct extent_buffer *leaf);
 int btrfs_cross_ref_exist(struct btrfs_trans_handle *trans,
@@ -2011,7 +2010,7 @@ void btrfs_delalloc_reserve_space(struct btrfs_root *root, struct inode *inode,
                                  u64 bytes);
 void btrfs_delalloc_free_space(struct btrfs_root *root, struct inode *inode,
                               u64 bytes);
-void btrfs_free_super_mirror_extents(struct btrfs_fs_info *info);
+void btrfs_free_pinned_extents(struct btrfs_fs_info *info);
 /* ctree.c */
 int btrfs_bin_search(struct extent_buffer *eb, struct btrfs_key *key,
                      int level, int *slot);