memcontrol: add vm_match_cgroup()

mm_cgroup() is exclusively used to test whether an mm's mem_cgroup pointer
is pointing to a specific cgroup.  Instead of returning the pointer, we can
just do the test itself in a new macro:

	vm_match_cgroup(mm, cgroup)

returns non-zero if the mm's mem_cgroup points to cgroup.  Otherwise it
returns zero.
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/memcontrol.h

@@ -51,10 +51,8 @@ extern int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
 					gfp_t gfp_mask);
 int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem);
 
-static inline struct mem_cgroup *mm_cgroup(const struct mm_struct *mm)
-{
-	return rcu_dereference(mm->mem_cgroup);
-}
+#define vm_match_cgroup(mm, cgroup)	\
+	((cgroup) == rcu_dereference((mm)->mem_cgroup))
 
 extern int mem_cgroup_prepare_migration(struct page *page);
 extern void mem_cgroup_end_migration(struct page *page);
@@ -123,9 +121,9 @@ static inline int mem_cgroup_cache_charge(struct page *page,
 	return 0;
 }
 
-static inline struct mem_cgroup *mm_cgroup(const struct mm_struct *mm)
+static inline int vm_match_cgroup(struct mm_struct *mm, struct mem_cgroup *mem)
 {
-	return NULL;
+	return 1;
 }
 
 static inline int task_in_mem_cgroup(struct task_struct *task,

mm/memcontrol.c

@@ -399,7 +399,7 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
 	int ret;
 
 	task_lock(task);
-	ret = task->mm && mm_cgroup(task->mm) == mem;
+	ret = task->mm && vm_match_cgroup(task->mm, mem);
 	task_unlock(task);
 	return ret;
 }

mm/rmap.c

@@ -321,7 +321,7 @@ static int page_referenced_anon(struct page *page,
 		 * counting on behalf of references from different
 		 * cgroups
 		 */
-		if (mem_cont && (mm_cgroup(vma->vm_mm) != mem_cont))
+		if (mem_cont && !vm_match_cgroup(vma->vm_mm, mem_cont))
 			continue;
 		referenced += page_referenced_one(page, vma, &mapcount);
 		if (!mapcount)
@@ -382,7 +382,7 @@ static int page_referenced_file(struct page *page,
 		 * counting on behalf of references from different
 		 * cgroups
 		 */
-		if (mem_cont && (mm_cgroup(vma->vm_mm) != mem_cont))
+		if (mem_cont && !vm_match_cgroup(vma->vm_mm, mem_cont))
 			continue;
 		if ((vma->vm_flags & (VM_LOCKED|VM_MAYSHARE))
 				  == (VM_LOCKED|VM_MAYSHARE)) {