Btrfs: add a rb_tree to improve performance of ulist search

Walking backref tree and btrfs quota rely on ulist very much.
This patch tries to use rb_tree to speed up search time.

The original code always checks whether an element
exists before adding a new element, however it costs O(n).

I try to add a rb_tree in the ulist,this is only used to speed up
search. I also do some measurements with quota enabled.

fsstress -p 4 -n 10000

Without this path:
real    0m51.058s       2m4.745s        1m28.222s       1m5.137s
user    0m0.035s        0m0.041s        0m0.105s        0m0.100s
sys     0m12.009s       0m11.246s       0m10.901s       0m10.999s       0m11.287s

With this path:
real    0m55.295s       0m50.960s       1m2.214s        0m48.273s
user    0m0.053s        0m0.095s        0m0.135s        0m0.107s
sys     0m7.766s        0m6.013s        0m6.319s        0m6.030s        0m6.532s

After applying the patch,the execute time is down by ~42%.(11.287s->6.532s)

Signed-off-by: Wang Shilong <wangsl-fnst@cn.fujitsu.com>
Reviewed-by: Miao Xie <miaox@cn.fujitsu.com>
Reviewed-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

diff --git a/fs/btrfs/ulist.c b/fs/btrfs/ulist.c
index ddc61cad008002eb2a06af77a4d10595376b37e1..7b417e20efe26da50a83a1a695e62491d3077f85 100644 (file)
--- a/fs/btrfs/ulist.c
+++ b/fs/btrfs/ulist.c
@@ -53,6 +53,7 @@ void ulist_init(struct ulist *ulist)
        ulist->nnodes = 0;
        ulist->nodes = ulist->int_nodes;
        ulist->nodes_alloced = ULIST_SIZE;
+       ulist->root = RB_ROOT;
 }
 EXPORT_SYMBOL(ulist_init);
 
@@ -72,6 +73,7 @@ void ulist_fini(struct ulist *ulist)
        if (ulist->nodes_alloced > ULIST_SIZE)
                kfree(ulist->nodes);
        ulist->nodes_alloced = 0;       /* in case ulist_fini is called twice */
+       ulist->root = RB_ROOT;
 }
 EXPORT_SYMBOL(ulist_fini);
 
@@ -123,6 +125,45 @@ void ulist_free(struct ulist *ulist)
 }
 EXPORT_SYMBOL(ulist_free);
 
+static struct ulist_node *ulist_rbtree_search(struct ulist *ulist, u64 val)
+{
+       struct rb_node *n = ulist->root.rb_node;
+       struct ulist_node *u = NULL;
+
+       while (n) {
+               u = rb_entry(n, struct ulist_node, rb_node);
+               if (u->val < val)
+                       n = n->rb_right;
+               else if (u->val > val)
+                       n = n->rb_left;
+               else
+                       return u;
+       }
+       return NULL;
+}
+
+static int ulist_rbtree_insert(struct ulist *ulist, struct ulist_node *ins)
+{
+       struct rb_node **p = &ulist->root.rb_node;
+       struct rb_node *parent = NULL;
+       struct ulist_node *cur = NULL;
+
+       while (*p) {
+               parent = *p;
+               cur = rb_entry(parent, struct ulist_node, rb_node);
+
+               if (cur->val < ins->val)
+                       p = &(*p)->rb_right;
+               else if (cur->val > ins->val)
+                       p = &(*p)->rb_left;
+               else
+                       return -EEXIST;
+       }
+       rb_link_node(&ins->rb_node, parent, p);
+       rb_insert_color(&ins->rb_node, &ulist->root);
+       return 0;
+}
+
 /**
  * ulist_add - add an element to the ulist
  * @ulist:     ulist to add the element to
@@ -151,14 +192,13 @@ 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 i;
-
-       for (i = 0; i < ulist->nnodes; ++i) {
-               if (ulist->nodes[i].val == val) {
-                       if (old_aux)
-                               *old_aux = ulist->nodes[i].aux;
-                       return 0;
-               }
+       int ret = 0;
+       struct ulist_node *node = NULL;
+       node = ulist_rbtree_search(ulist, val);
+       if (node) {
+               if (old_aux)
+                       *old_aux = node->aux;
+               return 0;
        }
 
        if (ulist->nnodes >= ulist->nodes_alloced) {
@@ -187,6 +227,8 @@ int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux,
        }
        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;
 
        return 1;

diff --git a/fs/btrfs/ulist.h b/fs/btrfs/ulist.h
index 21a1963439c3030c0146a1994f47a38fd43e0a95..fb36731074b5fa6ed5e27be3cca08caf329631ee 100644 (file)
--- a/fs/btrfs/ulist.h
+++ b/fs/btrfs/ulist.h
@@ -8,6 +8,9 @@
 #ifndef __ULIST__
 #define __ULIST__
 
+#include <linux/list.h>
+#include <linux/rbtree.h>
+
 /*
  * ulist is a generic data structure to hold a collection of unique u64
  * values. The only operations it supports is adding to the list and
@@ -34,6 +37,7 @@ struct ulist_iterator {
 struct ulist_node {
        u64 val;                /* value to store */
        u64 aux;                /* auxiliary value saved along with the val */
+       struct rb_node rb_node; /* used to speed up search */
 };
 
 struct ulist {
@@ -54,6 +58,8 @@ struct ulist {
         */
        struct ulist_node *nodes;
 
+       struct rb_root root;
+
        /*
         * inline storage space for the first ULIST_SIZE entries
         */