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Commit 54595fe2 authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
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memcg: use css_tryget in memcg 



From:KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

css_tryget() newly is added and we can know css is alive or not and get
refcnt of css in very safe way.  ("alive" here means "rmdir/destroy" is
not called.)

This patch replaces css_get() to css_tryget(), where I cannot explain
why css_get() is safe. And removes memcg->obsolete flag.

Reviewed-by: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a7ba0eef

mm/memcontrol.c

+62 −36
Original line number Diff line number Diff line
@@ -162,7 +162,6 @@ struct mem_cgroup { 
	 */

	bool use_hierarchy;

	unsigned long	last_oom_jiffies;

	int		obsolete;

	atomic_t	refcnt;



	unsigned int	swappiness;
@@ -283,6 +282,31 @@ struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p) 
				struct mem_cgroup, css);

}



static struct mem_cgroup *try_get_mem_cgroup_from_mm(struct mm_struct *mm)

{

	struct mem_cgroup *mem = NULL;

	/*

	 * Because we have no locks, mm->owner's may be being moved to other

	 * cgroup. We use css_tryget() here even if this looks

	 * pessimistic (rather than adding locks here).

	 */

	rcu_read_lock();

	do {

		mem = mem_cgroup_from_task(rcu_dereference(mm->owner));

		if (unlikely(!mem))

			break;

	} while (!css_tryget(&mem->css));

	rcu_read_unlock();

	return mem;

}



static bool mem_cgroup_is_obsolete(struct mem_cgroup *mem)

{

	if (!mem)

		return true;

	return css_is_removed(&mem->css);

}



/*

 * Following LRU functions are allowed to be used without PCG_LOCK.

 * Operations are called by routine of global LRU independently from memcg.
@@ -622,8 +646,9 @@ mem_cgroup_get_first_node(struct mem_cgroup *root_mem) 
{

	struct cgroup *cgroup;

	struct mem_cgroup *ret;

	bool obsolete = (root_mem->last_scanned_child &&

				root_mem->last_scanned_child->obsolete);

	bool obsolete;



	obsolete = mem_cgroup_is_obsolete(root_mem->last_scanned_child);



	/*

	 * Scan all children under the mem_cgroup mem
@@ -636,7 +661,7 @@ mem_cgroup_get_first_node(struct mem_cgroup *root_mem) 


	if (!root_mem->last_scanned_child || obsolete) {



		if (obsolete)

		if (obsolete && root_mem->last_scanned_child)

			mem_cgroup_put(root_mem->last_scanned_child);



		cgroup = list_first_entry(&root_mem->css.cgroup->children,
@@ -711,7 +736,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, 
	next_mem = mem_cgroup_get_first_node(root_mem);



	while (next_mem != root_mem) {

		if (next_mem->obsolete) {

		if (mem_cgroup_is_obsolete(next_mem)) {

			mem_cgroup_put(next_mem);

			cgroup_lock();

			next_mem = mem_cgroup_get_first_node(root_mem);
@@ -769,23 +794,17 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, 
	 * thread group leader migrates. It's possible that mm is not

	 * set, if so charge the init_mm (happens for pagecache usage).

	 */

	if (likely(!*memcg)) {

		rcu_read_lock();

		mem = mem_cgroup_from_task(rcu_dereference(mm->owner));

		if (unlikely(!mem)) {

			rcu_read_unlock();

			return 0;

		}

		/*

		 * For every charge from the cgroup, increment reference count

		 */

		css_get(&mem->css);

	mem = *memcg;

	if (likely(!mem)) {

		mem = try_get_mem_cgroup_from_mm(mm);

		*memcg = mem;

		rcu_read_unlock();

	} else {

		mem = *memcg;

		css_get(&mem->css);

	}

	if (unlikely(!mem))

		return 0;



	VM_BUG_ON(mem_cgroup_is_obsolete(mem));



	while (1) {

		int ret;
@@ -1072,12 +1091,19 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm, 
				MEM_CGROUP_CHARGE_TYPE_SHMEM, NULL);

}



/*

 * While swap-in, try_charge -> commit or cancel, the page is locked.

 * And when try_charge() successfully returns, one refcnt to memcg without

 * struct page_cgroup is aquired. This refcnt will be cumsumed by

 * "commit()" or removed by "cancel()"

 */

int mem_cgroup_try_charge_swapin(struct mm_struct *mm,

				 struct page *page,

				 gfp_t mask, struct mem_cgroup **ptr)

{

	struct mem_cgroup *mem;

	swp_entry_t     ent;

	int ret;



	if (mem_cgroup_disabled())

		return 0;
@@ -1096,10 +1122,15 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm, 
	ent.val = page_private(page);



	mem = lookup_swap_cgroup(ent);

	if (!mem || mem->obsolete)

	if (!mem)

		goto charge_cur_mm;

	if (!css_tryget(&mem->css))

		goto charge_cur_mm;

	*ptr = mem;

	return __mem_cgroup_try_charge(NULL, mask, ptr, true);

	ret = __mem_cgroup_try_charge(NULL, mask, ptr, true);

	/* drop extra refcnt from tryget */

	css_put(&mem->css);

	return ret;

charge_cur_mm:

	if (unlikely(!mm))

		mm = &init_mm;
@@ -1130,13 +1161,18 @@ int mem_cgroup_cache_charge_swapin(struct page *page, 
		ent.val = page_private(page);

		if (do_swap_account) {

			mem = lookup_swap_cgroup(ent);

			if (mem && mem->obsolete)

				mem = NULL;

			if (mem)

				mm = NULL;

			if (mem) {

				if (css_tryget(&mem->css))

					mm = NULL; /* charge to recorded */

				else

					mem = NULL; /* charge to current */

			}

		}

		ret = mem_cgroup_charge_common(page, mm, mask,

				MEM_CGROUP_CHARGE_TYPE_SHMEM, mem);

		/* drop extra refcnt from tryget */

		if (mem)

			css_put(&mem->css);



		if (!ret && do_swap_account) {

			/* avoid double counting */
@@ -1178,7 +1214,6 @@ void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr) 
		struct mem_cgroup *memcg;

		memcg = swap_cgroup_record(ent, NULL);

		if (memcg) {

			/* If memcg is obsolete, memcg can be != ptr */

			res_counter_uncharge(&memcg->memsw, PAGE_SIZE);

			mem_cgroup_put(memcg);

		}
@@ -1421,14 +1456,9 @@ int mem_cgroup_shrink_usage(struct mm_struct *mm, gfp_t gfp_mask) 
	if (!mm)

		return 0;



	rcu_read_lock();

	mem = mem_cgroup_from_task(rcu_dereference(mm->owner));

	if (unlikely(!mem)) {

		rcu_read_unlock();

	mem = try_get_mem_cgroup_from_mm(mm);

	if (unlikely(!mem))

		return 0;

	}

	css_get(&mem->css);

	rcu_read_unlock();



	do {

		progress = mem_cgroup_hierarchical_reclaim(mem, gfp_mask, true);
@@ -2086,9 +2116,6 @@ static struct mem_cgroup *mem_cgroup_alloc(void) 
 * the number of reference from swap_cgroup and free mem_cgroup when

 * it goes down to 0.

 *

 * When mem_cgroup is destroyed, mem->obsolete will be set to 0 and

 * entry which points to this memcg will be ignore at swapin.

 *

 * Removal of cgroup itself succeeds regardless of refs from swap.

 */
@@ -2174,7 +2201,6 @@ static void mem_cgroup_pre_destroy(struct cgroup_subsys *ss, 
					struct cgroup *cont)

{

	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);

	mem->obsolete = 1;

	mem_cgroup_force_empty(mem, false);

}