From adbe427b92d18cf3f801e82e9cd664fbe31cea3c Mon Sep 17 00:00:00 2001
From: Vladimir Davydov <vdavydov@parallels.com>
Date: Wed, 15 Apr 2015 16:13:00 -0700
Subject: [PATCH] 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: Vladimir Davydov <vdavydov@parallels.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
kernel/cgroup.c | 2 +-
mm/memcontrol.c | 24 ++++++++----------------
2 files changed, 9 insertions(+), 17 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index a220fdb66568e..59aa339a245c7 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -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
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c3f09b2dda5f9..0a06628470cc0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -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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