memcg: create extensible page stat update routines

Replace usage of the mem_cgroup_update_file_mapped() memcg
statistic update routine with two new routines:
* mem_cgroup_inc_page_stat()
* mem_cgroup_dec_page_stat()

As before, only the file_mapped statistic is managed. However, these more
general interfaces allow for new statistics to be more easily added. New
statistics are added with memcg dirty page accounting.

Signed-off-by: Greg Thelen <[e-mail]>
Signed-off-by: Andrea Righi <[e-mail]>
Acked-by: KAMEZAWA Hiroyuki <[e-mail]>
Acked-by: Daisuke Nishimura <[e-mail]>
Cc: Balbir Singh <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Wu Fengguang <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/memcontrol.h

···
 struct page;
 struct mm_struct;
 
+/* Stats that can be updated by kernel. */
+enum mem_cgroup_page_stat_item {
+	MEMCG_NR_FILE_MAPPED, /* # of pages charged as file rss */
+};
+
 extern unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
 					struct list_head *dst,
 					unsigned long *scanned, int order,
···
 	return false;
 }
 
-void mem_cgroup_update_file_mapped(struct page *page, int val);
+void mem_cgroup_update_page_stat(struct page *page,
+				 enum mem_cgroup_page_stat_item idx,
+				 int val);
+
+static inline void mem_cgroup_inc_page_stat(struct page *page,
+					    enum mem_cgroup_page_stat_item idx)
+{
+	mem_cgroup_update_page_stat(page, idx, 1);
+}
+
+static inline void mem_cgroup_dec_page_stat(struct page *page,
+					    enum mem_cgroup_page_stat_item idx)
+{
+	mem_cgroup_update_page_stat(page, idx, -1);
+}
+
 unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 						gfp_t gfp_mask);
 u64 mem_cgroup_get_limit(struct mem_cgroup *mem);
···
 {
 }
 
-static inline void mem_cgroup_update_file_mapped(struct page *page,
-							int val)
+static inline void mem_cgroup_inc_page_stat(struct page *page,
+					    enum mem_cgroup_page_stat_item idx)
+{
+}
+
+static inline void mem_cgroup_dec_page_stat(struct page *page,
+					    enum mem_cgroup_page_stat_item idx)
 {
 }
 

mm/memcontrol.c

···
  * possibility of race condition. If there is, we take a lock.
  */
 
-static void mem_cgroup_update_file_stat(struct page *page, int idx, int val)
+void mem_cgroup_update_page_stat(struct page *page,
+				 enum mem_cgroup_page_stat_item idx, int val)
 {
 	struct mem_cgroup *mem;
 	struct page_cgroup *pc = lookup_page_cgroup(page);
···
 			goto out;
 	}
 
-	this_cpu_add(mem->stat->count[idx], val);
-
 	switch (idx) {
-	case MEM_CGROUP_STAT_FILE_MAPPED:
+	case MEMCG_NR_FILE_MAPPED:
 		if (val > 0)
 			SetPageCgroupFileMapped(pc);
 		else if (!page_mapped(page))
 			ClearPageCgroupFileMapped(pc);
+		idx = MEM_CGROUP_STAT_FILE_MAPPED;
 		break;
 	default:
 		BUG();
 	}
+
+	this_cpu_add(mem->stat->count[idx], val);
 
 out:
 	if (unlikely(need_unlock))
···
 	rcu_read_unlock();
 	return;
 }
-
-void mem_cgroup_update_file_mapped(struct page *page, int val)
-{
-	mem_cgroup_update_file_stat(page, MEM_CGROUP_STAT_FILE_MAPPED, val);
-}
+EXPORT_SYMBOL(mem_cgroup_update_page_stat);
 
 /*
  * size of first charge trial. "32" comes from vmscan.c's magic value.

mm/rmap.c

···
 {
 	if (atomic_inc_and_test(&page->_mapcount)) {
 		__inc_zone_page_state(page, NR_FILE_MAPPED);
-		mem_cgroup_update_file_mapped(page, 1);
+		mem_cgroup_inc_page_stat(page, MEMCG_NR_FILE_MAPPED);
 	}
 }
 
···
 					      NR_ANON_TRANSPARENT_HUGEPAGES);
 	} else {
 		__dec_zone_page_state(page, NR_FILE_MAPPED);
-		mem_cgroup_update_file_mapped(page, -1);
+		mem_cgroup_dec_page_stat(page, MEMCG_NR_FILE_MAPPED);
 	}
 	/*
 	 * It would be tidy to reset the PageAnon mapping here,