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Commit 472b1053 authored by Li Zefan's avatar Li Zefan Committed by Linus Torvalds
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cgroups: use a hash table for css_set finding 



When we attach a process to a different cgroup, the css_set linked-list will
be run through to find a suitable existing css_set to use.  This patch
implements a hash table for better performance.

The following benchmarks have been tested:

For N in 1, 5, 10, 50, 100, 500, 1000, create N cgroups with one sleeping
task in each, and then move an additional task through each cgroup in
turn.

Here is a test result:

N	Loop	orig - Time(s)	hash - Time(s)
----------------------------------------------
1	10000	1.201231728	1.196311177
5	2000	1.065743872	1.040566424
10	1000	0.991054735	0.986876440
50	200	0.976554203	0.969608733
100	100	0.998504680	0.969218270
500	20	1.157347764	0.962602963
1000	10	1.619521852	1.085140172

Signed-off-by: default avatarLi Zefan <lizf@cn.fujitsu.com>
Reviewed-by: default avatarPaul Menage <menage@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 08ce5f16

include/linux/cgroup.h

+6 −1
Original line number Diff line number Diff line
@@ -155,6 +155,12 @@ struct css_set { 
	 */

	struct list_head list;



	/*

	 * List running through all cgroup groups in the same hash

	 * slot. Protected by css_set_lock

	 */

	struct hlist_node hlist;



	/*

	 * List running through all tasks using this cgroup

	 * group. Protected by css_set_lock
@@ -174,7 +180,6 @@ struct css_set { 
	 * during subsystem registration (at boot time).

	 */

	struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];



};



/*

kernel/cgroup.c

+47 −12
Original line number Diff line number Diff line
@@ -44,6 +44,7 @@ 
#include <linux/kmod.h>

#include <linux/delayacct.h>

#include <linux/cgroupstats.h>

#include <linux/hash.h>



#include <asm/atomic.h>
@@ -193,6 +194,27 @@ static struct cg_cgroup_link init_css_set_link; 
static DEFINE_RWLOCK(css_set_lock);

static int css_set_count;



/* hash table for cgroup groups. This improves the performance to

 * find an existing css_set */

#define CSS_SET_HASH_BITS	7

#define CSS_SET_TABLE_SIZE	(1 << CSS_SET_HASH_BITS)

static struct hlist_head css_set_table[CSS_SET_TABLE_SIZE];



static struct hlist_head *css_set_hash(struct cgroup_subsys_state *css[])

{

	int i;

	int index;

	unsigned long tmp = 0UL;



	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)

		tmp += (unsigned long)css[i];

	tmp = (tmp >> 16) ^ tmp;



	index = hash_long(tmp, CSS_SET_HASH_BITS);



	return &css_set_table[index];

}



/* We don't maintain the lists running through each css_set to its

 * task until after the first call to cgroup_iter_start(). This

 * reduces the fork()/exit() overhead for people who have cgroups
@@ -219,6 +241,7 @@ static int use_task_css_set_links; 
static void unlink_css_set(struct css_set *cg)

{

	write_lock(&css_set_lock);

	hlist_del(&cg->hlist);

	list_del(&cg->list);

	css_set_count--;

	while (!list_empty(&cg->cg_links)) {
@@ -284,9 +307,7 @@ static inline void put_css_set_taskexit(struct css_set *cg) 
/*

 * find_existing_css_set() is a helper for

 * find_css_set(), and checks to see whether an existing

 * css_set is suitable. This currently walks a linked-list for

 * simplicity; a later patch will use a hash table for better

 * performance

 * css_set is suitable.

 *

 * oldcg: the cgroup group that we're using before the cgroup

 * transition
@@ -303,7 +324,9 @@ static struct css_set *find_existing_css_set( 
{

	int i;

	struct cgroupfs_root *root = cgrp->root;

	struct list_head *l = &init_css_set.list;

	struct hlist_head *hhead;

	struct hlist_node *node;

	struct css_set *cg;



	/* Built the set of subsystem state objects that we want to

	 * see in the new css_set */
@@ -320,18 +343,13 @@ static struct css_set *find_existing_css_set( 
		}

	}



	/* Look through existing cgroup groups to find one to reuse */

	do {

		struct css_set *cg =

			list_entry(l, struct css_set, list);



	hhead = css_set_hash(template);

	hlist_for_each_entry(cg, node, hhead, hlist) {

		if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) {

			/* All subsystems matched */

			return cg;

		}

		/* Try the next cgroup group */

		l = l->next;

	} while (l != &init_css_set.list);

	}



	/* No existing cgroup group matched */

	return NULL;
@@ -393,6 +411,8 @@ static struct css_set *find_css_set( 
	struct list_head tmp_cg_links;

	struct cg_cgroup_link *link;



	struct hlist_head *hhead;



	/* First see if we already have a cgroup group that matches

	 * the desired set */

	write_lock(&css_set_lock);
@@ -417,6 +437,7 @@ static struct css_set *find_css_set( 
	kref_init(&res->ref);

	INIT_LIST_HEAD(&res->cg_links);

	INIT_LIST_HEAD(&res->tasks);

	INIT_HLIST_NODE(&res->hlist);



	/* Copy the set of subsystem state objects generated in

	 * find_existing_css_set() */
@@ -459,6 +480,11 @@ static struct css_set *find_css_set( 
	/* Link this cgroup group into the list */

	list_add(&res->list, &init_css_set.list);

	css_set_count++;



	/* Add this cgroup group to the hash table */

	hhead = css_set_hash(res->subsys);

	hlist_add_head(&res->hlist, hhead);



	write_unlock(&css_set_lock);



	return res;
@@ -2508,6 +2534,7 @@ int __init cgroup_init_early(void) 
	INIT_LIST_HEAD(&init_css_set.list);

	INIT_LIST_HEAD(&init_css_set.cg_links);

	INIT_LIST_HEAD(&init_css_set.tasks);

	INIT_HLIST_NODE(&init_css_set.hlist);

	css_set_count = 1;

	init_cgroup_root(&rootnode);

	list_add(&rootnode.root_list, &roots);
@@ -2520,6 +2547,9 @@ int __init cgroup_init_early(void) 
	list_add(&init_css_set_link.cg_link_list,

		 &init_css_set.cg_links);



	for (i = 0; i < CSS_SET_TABLE_SIZE; i++)

		INIT_HLIST_HEAD(&css_set_table[i]);



	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

		struct cgroup_subsys *ss = subsys[i];
@@ -2549,6 +2579,7 @@ int __init cgroup_init(void) 
{

	int err;

	int i;

	struct hlist_head *hhead;



	err = bdi_init(&cgroup_backing_dev_info);

	if (err)
@@ -2560,6 +2591,10 @@ int __init cgroup_init(void) 
			cgroup_init_subsys(ss);

	}



	/* Add init_css_set to the hash table */

	hhead = css_set_hash(init_css_set.subsys);

	hlist_add_head(&init_css_set.hlist, hhead);



	err = register_filesystem(&cgroup_fs_type);

	if (err < 0)

		goto out;