Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris...

[linux-2.6-omap-h63xx.git] / fs / btrfs / locking.c

diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 0cc314c10d66da148ee02d30ff1697b75f5c41ba..39bae7761db6c20ae87686a70d383a12c6285ee6 100644 (file)
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -25,6 +25,16 @@
 #include "extent_io.h"
 #include "locking.h"
 
+/*
+ * locks the per buffer mutex in an extent buffer.  This uses adaptive locks
+ * and the spin is not tuned very extensively.  The spinning does make a big
+ * difference in almost every workload, but spinning for the right amount of
+ * time needs some help.
+ *
+ * In general, we want to spin as long as the lock holder is doing btree
+ * searches, and we should give up if they are in more expensive code.
+ */
+
 int btrfs_tree_lock(struct extent_buffer *eb)
 {
        int i;
@@ -57,6 +67,10 @@ int btrfs_tree_locked(struct extent_buffer *eb)
        return mutex_is_locked(&eb->mutex);
 }
 
+/*
+ * btrfs_search_slot uses this to decide if it should drop its locks
+ * before doing something expensive like allocating free blocks for cow.
+ */
 int btrfs_path_lock_waiting(struct btrfs_path *path, int level)
 {
        int i;