mm: memcontrol: switch to native NR_FILE_PAGES and NR_SHMEM counters

Memcg maintains private MEMCG_CACHE and NR_SHMEM counters.  This
divergence from the generic VM accounting means unnecessary code overhead,
and creates a dependency for memcg that page->mapping is set up at the
time of charging, so that page types can be told apart.

Convert the generic accounting sites to mod_lruvec_page_state and friends
to maintain the per-cgroup vmstat counters of NR_FILE_PAGES and NR_SHMEM.
The page is already locked in these places, so page->mem_cgroup is stable;
we only need minimal tweaks of two mem_cgroup_migrate() calls to ensure
it's set up in time.

Then replace MEMCG_CACHE with NR_FILE_PAGES and delete the private
NR_SHMEM accounting sites.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Link: http://lkml.kernel.org/r/20200508183105.225460-10-hannes@cmpxchg.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/migrate.c

@@ -490,11 +490,18 @@ int migrate_page_move_mapping(struct address_space *mapping,
 	 * are mapped to swap space.
 	 */
 	if (newzone != oldzone) {
-		__dec_node_state(oldzone->zone_pgdat, NR_FILE_PAGES);
-		__inc_node_state(newzone->zone_pgdat, NR_FILE_PAGES);
+		struct lruvec *old_lruvec, *new_lruvec;
+		struct mem_cgroup *memcg;
+
+		memcg = page_memcg(page);
+		old_lruvec = mem_cgroup_lruvec(memcg, oldzone->zone_pgdat);
+		new_lruvec = mem_cgroup_lruvec(memcg, newzone->zone_pgdat);
+
+		__dec_lruvec_state(old_lruvec, NR_FILE_PAGES);
+		__inc_lruvec_state(new_lruvec, NR_FILE_PAGES);
 		if (PageSwapBacked(page) && !PageSwapCache(page)) {
-			__dec_node_state(oldzone->zone_pgdat, NR_SHMEM);
-			__inc_node_state(newzone->zone_pgdat, NR_SHMEM);
+			__dec_lruvec_state(old_lruvec, NR_SHMEM);
+			__inc_lruvec_state(new_lruvec, NR_SHMEM);
 		}
 		if (dirty && mapping_cap_account_dirty(mapping)) {
 			__dec_node_state(oldzone->zone_pgdat, NR_FILE_DIRTY);