Commit f7f82b81 authored by Wang Shilong's avatar Wang Shilong Committed by Josef Bacik
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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: default avatarWang Shilong <wangsl-fnst@cn.fujitsu.com>
Reviewed-by: default avatarMiao Xie <miaox@cn.fujitsu.com>
Reviewed-by: default avatarJan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: default avatarJosef Bacik <jbacik@fusionio.com>
parent c2c71324

fs/btrfs/ulist.c

+50 −8
Original line number Diff line number Diff line
@@ -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
@@ -151,15 +192,14 @@ 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) {

	int ret = 0;

	struct ulist_node *node = NULL;

	node = ulist_rbtree_search(ulist, val);

	if (node) {

		if (old_aux)

				*old_aux = ulist->nodes[i].aux;

			*old_aux = node->aux;

		return 0;

	}

	}



	if (ulist->nnodes >= ulist->nodes_alloced) {

		u64 new_alloced = ulist->nodes_alloced + 128;
@@ -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;

fs/btrfs/ulist.h

+6 −0
Original line number Diff line number Diff line
@@ -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

	 */

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