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>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/btrfs/ulist.h b/fs/btrfs/ulist.h
index 21a1963..fb36731 100644
--- 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
 	 */