Btrfs: Introduce contexts for metadata reservation

Introducing metadata reseravtion contexts has two major advantages.
First, it makes metadata reseravtion more traceable. Second, it can
reclaim freed space and re-add them to the itself after transaction
committed.

Besides add btrfs_block_rsv structure and related helper functions,
This patch contains following changes:

Move code that decides if freed tree block should be pinned into
btrfs_free_tree_block().

Make space accounting more accurate, mainly for handling read only
block groups.

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

1 files changed, 4 insertions, 4 deletions

diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 93c7ccb33118..56e728d70e39 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -45,13 +45,13 @@ struct btrfs_transaction {
 
 struct btrfs_trans_handle {
         u64 transid;
+        u64 block_group;
+        u64 bytes_reserved;
         unsigned long blocks_reserved;
         unsigned long blocks_used;
-        struct btrfs_transaction *transaction;
-        u64 block_group;
-        u64 alloc_exclude_start;
-        u64 alloc_exclude_nr;
         unsigned long delayed_ref_updates;
+        struct btrfs_transaction *transaction;
+        struct btrfs_block_rsv *block_rsv;
 };
 
 struct btrfs_pending_snapshot {