1 files changed, 88 insertions, 0 deletions

diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
new file mode 100644
index 000000000000..39bae7761db6
--- /dev/null
+++ b/fs/btrfs/locking.c
@@ -0,0 +1,88 @@
+/*
+ * Copyright (C) 2008 Oracle.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+#include <linux/sched.h>
+#include <linux/gfp.h>
+#include <linux/pagemap.h>
+#include <linux/spinlock.h>
+#include <linux/page-flags.h>
+#include <asm/bug.h>
+#include "ctree.h"
+#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;
+
+        if (mutex_trylock(&eb->mutex))
+                return 0;
+        for (i = 0; i < 512; i++) {
+                cpu_relax();
+                if (mutex_trylock(&eb->mutex))
+                        return 0;
+        }
+        cpu_relax();
+        mutex_lock_nested(&eb->mutex, BTRFS_MAX_LEVEL - btrfs_header_level(eb));
+        return 0;
+}
+
+int btrfs_try_tree_lock(struct extent_buffer *eb)
+{
+        return mutex_trylock(&eb->mutex);
+}
+
+int btrfs_tree_unlock(struct extent_buffer *eb)
+{
+        mutex_unlock(&eb->mutex);
+        return 0;
+}
+
+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;
+}
+