Btrfs: change reserved_extents to an atomic_t

We track delayed allocation per inodes via 2 counters, one is
outstanding_extents and reserved_extents.  Outstanding_extents is already an
atomic_t, but reserved_extents is not and is protected by a spinlock.  So
convert this to an atomic_t and instead of using a spinlock, use atomic_cmpxchg
when releasing delalloc bytes.  This makes our inode 72 bytes smaller, and
reduces locking overhead (albiet it was minimal to begin with).  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 1 insertions, 2 deletions

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index ccc991c542df..57c3bb2884ce 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -136,9 +136,8 @@ struct btrfs_inode {
          * items we think we'll end up using, and reserved_extents is the number
          * of extent items we've reserved metadata for.
          */
-        spinlock_t accounting_lock;
         atomic_t outstanding_extents;
-        int reserved_extents;
+        atomic_t reserved_extents;
 
         /*
          * ordered_data_close is set by truncate when a file that used