Btrfs: Optimize locking in btrfs_next_leaf()

btrfs_next_leaf was using blocking locks when it could have been using
faster spinning ones instead.  This adds a few extra checks around
the pieces that block and switches over to spinning locks.

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

1 files changed, 65 insertions, 23 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 271b05e507d7..b8082762ca78 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -4127,28 +4127,44 @@ next:
 int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
 {
         int slot;
-        int level = 1;
+        int level;
         struct extent_buffer *c;
-        struct extent_buffer *next = NULL;
+        struct extent_buffer *next;
         struct btrfs_key key;
         u32 nritems;
         int ret;
+        int old_spinning = path->leave_spinning;
+        int force_blocking = 0;
 
         nritems = btrfs_header_nritems(path->nodes[0]);
         if (nritems == 0)
                 return 1;
 
-        btrfs_item_key_to_cpu(path->nodes[0], &key, nritems - 1);
+        /*
+         * we take the blocks in an order that upsets lockdep.  Using
+         * blocking mode is the only way around it.
+         */
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+        force_blocking = 1;
+#endif
 
+        btrfs_item_key_to_cpu(path->nodes[0], &key, nritems - 1);
+again:
+        level = 1;
+        next = NULL;
         btrfs_release_path(root, path);
+
         path->keep_locks = 1;
+
+        if (!force_blocking)
+                path->leave_spinning = 1;
+
         ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
         path->keep_locks = 0;
 
         if (ret < 0)
                 return ret;
 
-        btrfs_set_path_blocking(path);
         nritems = btrfs_header_nritems(path->nodes[0]);
         /*
          * by releasing the path above we dropped all our locks.  A balance
@@ -4158,19 +4174,24 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
          */
         if (nritems > 0 && path->slots[0] < nritems - 1) {
                 path->slots[0]++;
+                ret = 0;
                 goto done;
         }
 
         while (level < BTRFS_MAX_LEVEL) {
-                if (!path->nodes[level])
-                        return 1;
+                if (!path->nodes[level]) {
+                        ret = 1;
+                        goto done;
+                }
 
                 slot = path->slots[level] + 1;
                 c = path->nodes[level];
                 if (slot >= btrfs_header_nritems(c)) {
                         level++;
-                        if (level == BTRFS_MAX_LEVEL)
-                                return 1;
+                        if (level == BTRFS_MAX_LEVEL) {
+                                ret = 1;
+                                goto done;
+                        }
                         continue;
                 }
 
@@ -4179,16 +4200,22 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
                         free_extent_buffer(next);
                 }
 
-                /* the path was set to blocking above */
-                if (level == 1 && (path->locks[1] || path->skip_locking) &&
-                    path->reada)
-                        reada_for_search(root, path, level, slot, 0);
+                next = c;
+                ret = read_block_for_search(NULL, root, path, &next, level,
+                                            slot, &key);
+                if (ret == -EAGAIN)
+                        goto again;
 
-                next = read_node_slot(root, c, slot);
                 if (!path->skip_locking) {
-                        btrfs_assert_tree_locked(c);
-                        btrfs_tree_lock(next);
-                        btrfs_set_lock_blocking(next);
+                        ret = btrfs_try_spin_lock(next);
+                        if (!ret) {
+                                btrfs_set_path_blocking(path);
+                                btrfs_tree_lock(next);
+                                if (!force_blocking)
+                                        btrfs_clear_path_blocking(path, next);
+                        }
+                        if (force_blocking)
+                                btrfs_set_lock_blocking(next);
                 }
                 break;
         }
@@ -4198,27 +4225,42 @@ int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
                 c = path->nodes[level];
                 if (path->locks[level])
                         btrfs_tree_unlock(c);
+
                 free_extent_buffer(c);
                 path->nodes[level] = next;
                 path->slots[level] = 0;
                 if (!path->skip_locking)
                         path->locks[level] = 1;
+
                 if (!level)
                         break;
 
-                btrfs_set_path_blocking(path);
-                if (level == 1 && path->locks[1] && path->reada)
-                        reada_for_search(root, path, level, slot, 0);
-                next = read_node_slot(root, next, 0);
+                ret = read_block_for_search(NULL, root, path, &next, level,
+                                            0, &key);
+                if (ret == -EAGAIN)
+                        goto again;
+
                 if (!path->skip_locking) {
                         btrfs_assert_tree_locked(path->nodes[level]);
-                        btrfs_tree_lock(next);
-                        btrfs_set_lock_blocking(next);
+                        ret = btrfs_try_spin_lock(next);
+                        if (!ret) {
+                                btrfs_set_path_blocking(path);
+                                btrfs_tree_lock(next);
+                                if (!force_blocking)
+                                        btrfs_clear_path_blocking(path, next);
+                        }
+                        if (force_blocking)
+                                btrfs_set_lock_blocking(next);
                 }
         }
+        ret = 0;
 done:
         unlock_up(path, 0, 1);
-        return 0;
+        path->leave_spinning = old_spinning;
+        if (!old_spinning)
+                btrfs_set_path_blocking(path);
+
+        return ret;
 }
 
 /*