X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=fs%2Fbtrfs%2Flocking.c;h=e30aa6e2958fee23b12553764f78cac4b993ebb1;hb=52c2617990fed072220708d6b771dc10f37547b0;hp=d617c29787fac22cf5d79dcf7f1aa4eed19085b4;hpb=4881ee5a2e995c6a8999b56de70aa3834369d8ee;p=safe%2Fjmp%2Flinux-2.6

diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index d617c29..e30aa6e 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -25,6 +25,15 @@
 #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;
@@ -57,3 +66,22 @@ 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;
+	struct extent_buffer *eb;
+	for (i = level; i <= level + 1 && i < BTRFS_MAX_LEVEL; i++) {
+		eb = path->nodes[i];
+		if (!eb)
+			break;
+		smp_mb();
+		if (!list_empty(&eb->mutex.wait_list))
+			return 1;
+	}
+	return 0;
+}
+