mm: memcg: remove unneeded shmem charge type

shmem page charges have not needed a separate charge type to tell them
from regular file pages since 08e552c6 ("memcg: synchronized LRU").
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Wanpeng Li <liwp.linux@gmail.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -379,7 +379,6 @@ static bool move_file(void)
 enum charge_type {
 	MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
 	MEM_CGROUP_CHARGE_TYPE_ANON,
-	MEM_CGROUP_CHARGE_TYPE_SHMEM,	/* used by page migration of shmem */
 	MEM_CGROUP_CHARGE_TYPE_SWAPOUT,	/* for accounting swapcache */
 	MEM_CGROUP_CHARGE_TYPE_DROP,	/* a page was unused swap cache */
 	NR_CHARGE_TYPE,
@@ -2902,8 +2901,6 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
 
 	if (unlikely(!mm))
 		mm = &init_mm;
-	if (!page_is_file_cache(page))
-		type = MEM_CGROUP_CHARGE_TYPE_SHMEM;
 
 	if (!PageSwapCache(page))
 		ret = mem_cgroup_charge_common(page, mm, gfp_mask, type);
@@ -3310,10 +3307,8 @@ void mem_cgroup_prepare_migration(struct page *page, struct page *newpage,
 	 */
 	if (PageAnon(page))
 		ctype = MEM_CGROUP_CHARGE_TYPE_ANON;
-	else if (page_is_file_cache(page))
-		ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
 	else
-		ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
+		ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
 	/*
 	 * The page is committed to the memcg, but it's not actually
 	 * charged to the res_counter since we plan on replacing the
@@ -3407,10 +3402,6 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
 	 */
 	if (!memcg)
 		return;
-
-	if (PageSwapBacked(oldpage))
-		type = MEM_CGROUP_CHARGE_TYPE_SHMEM;
-
 	/*
 	 * Even if newpage->mapping was NULL before starting replacement,
 	 * the newpage may be on LRU(or pagevec for LRU) already. We lock