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>

2 files changed, 55 insertions, 88 deletions

diff --git a/fs/btrfs/ulist.c b/fs/btrfs/ulist.c
index 35f5de9dd498..8dd0e8dfdaf4 100644
--- a/fs/btrfs/ulist.c
+++ b/fs/btrfs/ulist.c
@@ -7,6 +7,7 @@
 #include <linux/slab.h>
 #include <linux/export.h>
 #include "ulist.h"
+#include "ctree.h"
 
 /*
  * ulist is a generic data structure to hold a collection of unique u64
@@ -14,10 +15,6 @@
  * 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.
- *
  * A sample usage for ulists is the enumeration of directed graphs without
  * visiting a node twice. The pseudo-code could look like this:
  *
@@ -50,10 +47,9 @@
  */
 void ulist_init(struct ulist *ulist)
 {
-        ulist->nnodes = 0;
-        ulist->nodes = ulist->int_nodes;
-        ulist->nodes_alloced = ULIST_SIZE;
+        INIT_LIST_HEAD(&ulist->nodes);
         ulist->root = RB_ROOT;
+        ulist->nnodes = 0;
 }
 EXPORT_SYMBOL(ulist_init);
 
@@ -66,14 +62,14 @@ EXPORT_SYMBOL(ulist_init);
  */
 void ulist_fini(struct ulist *ulist)
 {
-        /*
-         * The first ULIST_SIZE elements are stored inline in struct ulist.
-         * Only if more elements are alocated they need to be freed.
-         */
-        if (ulist->nodes_alloced > ULIST_SIZE)
-                kfree(ulist->nodes);
-        ulist->nodes_alloced = 0;       /* in case ulist_fini is called twice */
+        struct ulist_node *node;
+        struct ulist_node *next;
+
+        list_for_each_entry_safe(node, next, &ulist->nodes, list) {
+                kfree(node);
+        }
         ulist->root = RB_ROOT;
+        INIT_LIST_HEAD(&ulist->nodes);
 }
 EXPORT_SYMBOL(ulist_fini);
 
@@ -192,57 +188,29 @@ int ulist_add(struct ulist *ulist, u64 val, u64 aux, gfp_t gfp_mask)
 int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux,
                     u64 *old_aux, gfp_t gfp_mask)
 {
-        int ret = 0;
-        struct ulist_node *node = NULL;
+        int ret;
+        struct ulist_node *node;
+
         node = ulist_rbtree_search(ulist, val);
         if (node) {
                 if (old_aux)
                         *old_aux = node->aux;
                 return 0;
         }
+        node = kmalloc(sizeof(*node), gfp_mask);
+        if (!node)
+                return -ENOMEM;
 
-        if (ulist->nnodes >= ulist->nodes_alloced) {
-                u64 new_alloced = ulist->nodes_alloced + 128;
-                struct ulist_node *new_nodes;
-                void *old = NULL;
-                int i;
-
-                /*
-                 * if nodes_alloced == ULIST_SIZE no memory has been allocated
-                 * yet, so pass NULL to krealloc
-                 */
-                if (ulist->nodes_alloced > ULIST_SIZE)
-                        old = ulist->nodes;
+        node->val = val;
+        node->aux = aux;
+#ifdef CONFIG_BTRFS_DEBUG
+        node->seqnum = ulist->nnodes;
+#endif
 
-                new_nodes = krealloc(old, sizeof(*new_nodes) * new_alloced,
-                                     gfp_mask);
-                if (!new_nodes)
-                        return -ENOMEM;
-
-                if (!old)
-                        memcpy(new_nodes, ulist->int_nodes,
-                               sizeof(ulist->int_nodes));
-
-                ulist->nodes = new_nodes;
-                ulist->nodes_alloced = new_alloced;
-
-                /*
-                 * krealloc actually uses memcpy, which does not copy rb_node
-                 * pointers, so we have to do it ourselves.  Otherwise we may
-                 * be bitten by crashes.
-                 */
-                ulist->root = RB_ROOT;
-                for (i = 0; i < ulist->nnodes; i++) {
-                        ret = ulist_rbtree_insert(ulist, &ulist->nodes[i]);
-                        if (ret < 0)
-                                return ret;
-                }
-        }
-        ulist->nodes[ulist->nnodes].val = val;
-        ulist->nodes[ulist->nnodes].aux = aux;
-        ret = ulist_rbtree_insert(ulist, &ulist->nodes[ulist->nnodes]);
-        BUG_ON(ret);
-        ++ulist->nnodes;
+        ret = ulist_rbtree_insert(ulist, node);
+        ASSERT(!ret);
+        list_add_tail(&node->list, &ulist->nodes);
+        ulist->nnodes++;
 
         return 1;
 }
@@ -266,11 +234,26 @@ EXPORT_SYMBOL(ulist_add);
  */
 struct ulist_node *ulist_next(struct ulist *ulist, struct ulist_iterator *uiter)
 {
-        if (ulist->nnodes == 0)
+        struct ulist_node *node;
+
+        if (list_empty(&ulist->nodes))
                 return NULL;
-        if (uiter->i < 0 || uiter->i >= ulist->nnodes)
+        if (uiter->cur_list && uiter->cur_list->next == &ulist->nodes)
                 return NULL;
-
-        return &ulist->nodes[uiter->i++];
+        if (uiter->cur_list) {
+                uiter->cur_list = uiter->cur_list->next;
+        } else {
+                uiter->cur_list = ulist->nodes.next;
+#ifdef CONFIG_BTRFS_DEBUG
+                uiter->i = 0;
+#endif
+        }
+        node = list_entry(uiter->cur_list, struct ulist_node, list);
+#ifdef CONFIG_BTRFS_DEBUG
+        ASSERT(node->seqnum == uiter->i);
+        ASSERT(uiter->i >= 0 && uiter->i < ulist->nnodes);
+        uiter->i++;
+#endif
+        return node;
 }
 EXPORT_SYMBOL(ulist_next);
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