Commit adbe427b authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
Browse files

memcg: zap mem_cgroup_lookup() 



mem_cgroup_lookup() is a wrapper around mem_cgroup_from_id(), which
checks that id != 0 before issuing the function call.  Today, there is
no point in this additional check apart from optimization, because there
is no css with id <= 0, so that css_from_id, called by
mem_cgroup_from_id, will return NULL for any id <= 0.

Since mem_cgroup_from_id is only called from mem_cgroup_lookup, let us
zap mem_cgroup_lookup, substituting calls to it with mem_cgroup_from_id
and moving the check if id > 0 to css_from_id.

Signed-off-by: default avatarVladimir Davydov <vdavydov@parallels.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d7e4a2ea

kernel/cgroup.c

+1 −1
Original line number Diff line number Diff line
@@ -5451,7 +5451,7 @@ struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry, 
struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss)

{

	WARN_ON_ONCE(!rcu_read_lock_held());

	return idr_find(&ss->css_idr, id);

	return id > 0 ? idr_find(&ss->css_idr, id) : NULL;

}



#ifdef CONFIG_CGROUP_DEBUG

mm/memcontrol.c

+8 −16
Original line number Diff line number Diff line
@@ -460,6 +460,12 @@ static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg) 
	return memcg->css.id;

}



/*

 * A helper function to get mem_cgroup from ID. must be called under

 * rcu_read_lock().  The caller is responsible for calling

 * css_tryget_online() if the mem_cgroup is used for charging. (dropping

 * refcnt from swap can be called against removed memcg.)

 */

static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id)

{

	struct cgroup_subsys_state *css;
@@ -2348,20 +2354,6 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages) 
	css_put_many(&memcg->css, nr_pages);

}



/*

 * A helper function to get mem_cgroup from ID. must be called under

 * rcu_read_lock().  The caller is responsible for calling

 * css_tryget_online() if the mem_cgroup is used for charging. (dropping

 * refcnt from swap can be called against removed memcg.)

 */

static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)

{

	/* ID 0 is unused ID */

	if (!id)

		return NULL;

	return mem_cgroup_from_id(id);

}



/*

 * try_get_mem_cgroup_from_page - look up page's memcg association

 * @page: the page
@@ -2388,7 +2380,7 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page) 
		ent.val = page_private(page);

		id = lookup_swap_cgroup_id(ent);

		rcu_read_lock();

		memcg = mem_cgroup_lookup(id);

		memcg = mem_cgroup_from_id(id);

		if (memcg && !css_tryget_online(&memcg->css))

			memcg = NULL;

		rcu_read_unlock();
@@ -5869,7 +5861,7 @@ void mem_cgroup_uncharge_swap(swp_entry_t entry) 


	id = swap_cgroup_record(entry, 0);

	rcu_read_lock();

	memcg = mem_cgroup_lookup(id);

	memcg = mem_cgroup_from_id(id);

	if (memcg) {

		if (!mem_cgroup_is_root(memcg))

			page_counter_uncharge(&memcg->memsw, 1);

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