memcg: move do_memsw_account() to CONFIG_MEMCG_V1

The do_memsw_account() is used to enable or disable legacy memory+swap
accounting in memory cgroup.  However with disabled CONFIG_MEMCG_V1, we
don't need to keep checking it.  So, let's always return false for
!CONFIG_MEMCG_V1 configs.

Before the patch:

$ size mm/memcontrol.o
   text    data     bss     dec     hex filename
  49928   10736    4172   64836    fd44 mm/memcontrol.o

After the patch:

$ size mm/memcontrol.o
   text    data     bss     dec     hex filename
  49430   10480    4172   64082    fa52 mm/memcontrol.o

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Shakeel Butt <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Roman Gushchin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: shakeelb

mm/memcontrol-v1.h

@@ -22,12 +22,6 @@
 	     iter != NULL;				\
 	     iter = mem_cgroup_iter(NULL, iter, NULL))
 
-/* Whether legacy memory+swap accounting is active */
-static inline bool do_memsw_account(void)
-{
-	return !cgroup_subsys_on_dfl(memory_cgrp_subsys);
-}
-
 unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap);
 
 void drain_all_stock(struct mem_cgroup *root_memcg);
@@ -42,6 +36,12 @@ struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg);
 /* Cgroup v1-specific declarations */
 #ifdef CONFIG_MEMCG_V1
 
+/* Whether legacy memory+swap accounting is active */
+static inline bool do_memsw_account(void)
+{
+	return !cgroup_subsys_on_dfl(memory_cgrp_subsys);
+}
+
 unsigned long memcg_events_local(struct mem_cgroup *memcg, int event);
 unsigned long memcg_page_state_local(struct mem_cgroup *memcg, int idx);
 unsigned long memcg_page_state_local_output(struct mem_cgroup *memcg, int item);
@@ -94,6 +94,7 @@ extern struct cftype mem_cgroup_legacy_files[];
 
 #else	/* CONFIG_MEMCG_V1 */
 
+static inline bool do_memsw_account(void) { return false; }
 static inline bool memcg1_alloc_events(struct mem_cgroup *memcg) { return true; }
 static inline void memcg1_free_events(struct mem_cgroup *memcg) {}