Btrfs: rework ulist with list+rb_tree

We are really suffering from now ulist's implementation, some developers
gave their try, and i just gave some of my ideas for things:

 1. use list+rb_tree instead of arrary+rb_tree

 2. add cur_list to iterator rather than ulist structure.

 3. add seqnum into every node when they are added, this is
 used to do selfcheck when iterating node.

I noticed Zach Brown's comments before, long term is to kick off
ulist implementation, however, for now, we need at least avoid
arrary from ulist.

Cc: Liu Bo <bo.li.liu@oracle.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Zach Brown <zab@redhat.com>
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 11 insertions, 27 deletions

diff --git a/fs/btrfs/ulist.h b/fs/btrfs/ulist.h
index fb36731074b5..2be7102d8073 100644
--- a/fs/btrfs/ulist.h
+++ b/fs/btrfs/ulist.h
@@ -17,18 +17,12 @@
  * enumerating it.
  * It is possible to store an auxiliary value along with the key.
  *
- * The implementation is preliminary and can probably be sped up
- * significantly. A first step would be to store the values in an rbtree
- * as soon as ULIST_SIZE is exceeded.
  */
-
-/*
- * number of elements statically allocated inside struct ulist
- */
-#define ULIST_SIZE 16
-
 struct ulist_iterator {
+#ifdef CONFIG_BTRFS_DEBUG
 	int i;
+#endif
+	struct list_head *cur_list;  /* hint to start search */
 };
 
 /*
@@ -37,6 +31,12 @@ struct ulist_iterator {
 struct ulist_node {
 	u64 val;		/* value to store */
 	u64 aux;		/* auxiliary value saved along with the val */
+
+#ifdef CONFIG_BTRFS_DEBUG
+	int seqnum;		/* sequence number this node is added */
+#endif
+
+	struct list_head list;  /* used to link node */
 	struct rb_node rb_node;	/* used to speed up search */
 };
 
@@ -46,24 +46,8 @@ struct ulist {
 	 */
 	unsigned long nnodes;
 
-	/*
-	 * number of nodes we already have room for
-	 */
-	unsigned long nodes_alloced;
-
-	/*
-	 * pointer to the array storing the elements. The first ULIST_SIZE
-	 * elements are stored inline. In this case the it points to int_nodes.
-	 * After exceeding ULIST_SIZE, dynamic memory is allocated.
-	 */
-	struct ulist_node *nodes;
-
+	struct list_head nodes;
 	struct rb_root root;
-
-	/*
-	 * inline storage space for the first ULIST_SIZE entries
-	 */
-	struct ulist_node int_nodes[ULIST_SIZE];
 };
 
 void ulist_init(struct ulist *ulist);
@@ -77,6 +61,6 @@ int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux,
 struct ulist_node *ulist_next(struct ulist *ulist,
 			      struct ulist_iterator *uiter);
 
-#define ULIST_ITER_INIT(uiter) ((uiter)->i = 0)
+#define ULIST_ITER_INIT(uiter) ((uiter)->cur_list = NULL)
 
 #endif