memcg: rename and export try_get_mem_cgroup_from_page()

So that the hwpoison injector can get mem_cgroup for arbitrary page
and thus know whether it is owned by some mem_cgroup task(s).

[AK: Merged with latest git tree]

CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
CC: Hugh Dickins <hugh.dickins@tiscali.co.uk>
CC: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
CC: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

2 files changed, 10 insertions, 7 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index bf9213b2db8f..fc9bae82ac42 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -68,6 +68,7 @@ extern unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
 extern void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask);
 int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem);
 
+extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
 extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
 
 static inline
@@ -189,6 +190,11 @@ mem_cgroup_move_lists(struct page *page, enum lru_list from, enum lru_list to)
 {
 }
 
+static inline struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
+{
+        return NULL;
+}
+
 static inline int mm_match_cgroup(struct mm_struct *mm, struct mem_cgroup *mem)
 {
         return 1;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e0c2066495e3..b5ac61ce7346 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1379,25 +1379,22 @@ static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
         return container_of(css, struct mem_cgroup, css);
 }
 
-static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page)
+struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
 {
-        struct mem_cgroup *mem;
+        struct mem_cgroup *mem = NULL;
         struct page_cgroup *pc;
         unsigned short id;
         swp_entry_t ent;
 
         VM_BUG_ON(!PageLocked(page));
 
-        if (!PageSwapCache(page))
-                return NULL;
-
         pc = lookup_page_cgroup(page);
         lock_page_cgroup(pc);
         if (PageCgroupUsed(pc)) {
                 mem = pc->mem_cgroup;
                 if (mem && !css_tryget(&mem->css))
                         mem = NULL;
-        } else {
+        } else if (PageSwapCache(page)) {
                 ent.val = page_private(page);
                 id = lookup_swap_cgroup(ent);
                 rcu_read_lock();
@@ -1743,7 +1740,7 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm,
          */
         if (!PageSwapCache(page))
                 goto charge_cur_mm;
-        mem = try_get_mem_cgroup_from_swapcache(page);
+        mem = try_get_mem_cgroup_from_page(page);
         if (!mem)
                 goto charge_cur_mm;
         *ptr = mem;