memcg: allocate v1 event percpu only on v1 deployment

Currently memcg->events_percpu gets allocated on v2 deployments.  Let's
move the allocation to v1 only codebase.  This is not needed in v2.

Link: https://lkml.kernel.org/r/20240815050453.1298138-7-shakeel.butt@linux.devSigned-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/memcontrol.h

@@ -255,7 +255,6 @@ struct mem_cgroup {
 	struct list_head objcg_list;
 
 	struct memcg_vmstats_percpu __percpu *vmstats_percpu;
-	struct memcg1_events_percpu __percpu *events_percpu;
 
 #ifdef CONFIG_CGROUP_WRITEBACK
 	struct list_head cgwb_list;
@@ -277,6 +276,8 @@ struct mem_cgroup {
 	struct page_counter kmem;		/* v1 only */
 	struct page_counter tcpmem;		/* v1 only */
 
+	struct memcg1_events_percpu __percpu *events_percpu;
+
 	unsigned long soft_limit;
 
 	/* protected by memcg_oom_lock */

mm/memcontrol-v1.c

@@ -1442,6 +1442,12 @@ static void mem_cgroup_threshold(struct mem_cgroup *memcg)
 	}
 }
 
+/* Cgroup1: threshold notifications & softlimit tree updates */
+struct memcg1_events_percpu {
+	unsigned long nr_page_events;
+	unsigned long targets[MEM_CGROUP_NTARGETS];
+};
+
 static void memcg1_charge_statistics(struct mem_cgroup *memcg, int nr_pages)
 {
 	/* pagein of a big page is an event. So, ignore page size */
@@ -3033,6 +3039,19 @@ bool memcg1_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,
 	return false;
 }
 
+bool memcg1_alloc_events(struct mem_cgroup *memcg)
+{
+	memcg->events_percpu = alloc_percpu_gfp(struct memcg1_events_percpu,
+						GFP_KERNEL_ACCOUNT);
+	return !!memcg->events_percpu;
+}
+
+void memcg1_free_events(struct mem_cgroup *memcg)
+{
+	if (memcg->events_percpu)
+		free_percpu(memcg->events_percpu);
+}
+
 static int __init memcg1_init(void)
 {
 	int node;

mm/memcontrol-v1.h

@@ -55,12 +55,6 @@ enum mem_cgroup_events_target {
 	MEM_CGROUP_NTARGETS,
 };
 
-/* Cgroup1: threshold notifications & softlimit tree updates */
-struct memcg1_events_percpu {
-	unsigned long nr_page_events;
-	unsigned long targets[MEM_CGROUP_NTARGETS];
-};
-
 unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap);
 
 void drain_all_stock(struct mem_cgroup *root_memcg);
@@ -72,21 +66,12 @@ unsigned long memcg_page_state_output(struct mem_cgroup *memcg, int item);
 unsigned long memcg_page_state_local_output(struct mem_cgroup *memcg, int item);
 int memory_stat_show(struct seq_file *m, void *v);
 
-static inline bool memcg1_alloc_events(struct mem_cgroup *memcg)
-{
-	memcg->events_percpu = alloc_percpu_gfp(struct memcg1_events_percpu,
-						GFP_KERNEL_ACCOUNT);
-	return !!memcg->events_percpu;
-}
-
-static inline void memcg1_free_events(struct mem_cgroup *memcg)
-{
-	if (memcg->events_percpu)
-		free_percpu(memcg->events_percpu);
-}
-
 /* Cgroup v1-specific declarations */
 #ifdef CONFIG_MEMCG_V1
+
+bool memcg1_alloc_events(struct mem_cgroup *memcg);
+void memcg1_free_events(struct mem_cgroup *memcg);
+
 void memcg1_memcg_init(struct mem_cgroup *memcg);
 void memcg1_remove_from_trees(struct mem_cgroup *memcg);
 
@@ -139,6 +124,9 @@ extern struct cftype mem_cgroup_legacy_files[];
 
 #else	/* CONFIG_MEMCG_V1 */
 
+static inline bool memcg1_alloc_events(struct mem_cgroup *memcg) { return true; }
+static inline void memcg1_free_events(struct mem_cgroup *memcg) {}
+
 static inline void memcg1_memcg_init(struct mem_cgroup *memcg) {}
 static inline void memcg1_remove_from_trees(struct mem_cgroup *memcg) {}
 static inline void memcg1_soft_limit_reset(struct mem_cgroup *memcg) {}