mm: memcg: move legacy memcg event code into memcontrol-v1.c

Cgroup v1's memory controller contains a pretty complicated event
notifications mechanism which is not used on cgroup v2.  Let's move the
corresponding code into memcontrol-v1.c.

Please, note, that mem_cgroup_event_ratelimit() remains in memcontrol.c,
otherwise it would require exporting too many details on memcg stats
outside of memcontrol.c.

Link: https://lkml.kernel.org/r/20240625005906.106920-7-roman.gushchin@linux.dev
Signed-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/memcontrol.h

@@ -69,18 +69,6 @@ struct mem_cgroup_id {
 	refcount_t ref;
 };
 
-/*
- * Per memcg event counter is incremented at every pagein/pageout. With THP,
- * it will be incremented by the number of pages. This counter is used
- * to trigger some periodic events. This is straightforward and better
- * than using jiffies etc. to handle periodic memcg event.
- */
-enum mem_cgroup_events_target {
-	MEM_CGROUP_TARGET_THRESH,
-	MEM_CGROUP_TARGET_SOFTLIMIT,
-	MEM_CGROUP_NTARGETS,
-};
-
 struct memcg_vmstats_percpu;
 struct memcg_vmstats;
 struct lruvec_stats_percpu;

mm/memcontrol-v1.h

@@ -41,4 +41,55 @@ u64 mem_cgroup_move_charge_read(struct cgroup_subsys_state *css,
 int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css,
 				 struct cftype *cft, u64 val);
 
+/*
+ * Per memcg event counter is incremented at every pagein/pageout. With THP,
+ * it will be incremented by the number of pages. This counter is used
+ * to trigger some periodic events. This is straightforward and better
+ * than using jiffies etc. to handle periodic memcg event.
+ */
+enum mem_cgroup_events_target {
+	MEM_CGROUP_TARGET_THRESH,
+	MEM_CGROUP_TARGET_SOFTLIMIT,
+	MEM_CGROUP_NTARGETS,
+};
+
+/* Whether legacy memory+swap accounting is active */
+static bool do_memsw_account(void)
+{
+	return !cgroup_subsys_on_dfl(memory_cgrp_subsys);
+}
+
+/*
+ * Iteration constructs for visiting all cgroups (under a tree).  If
+ * loops are exited prematurely (break), mem_cgroup_iter_break() must
+ * be used for reference counting.
+ */
+#define for_each_mem_cgroup_tree(iter, root)		\
+	for (iter = mem_cgroup_iter(root, NULL, NULL);	\
+	     iter != NULL;				\
+	     iter = mem_cgroup_iter(root, iter, NULL))
+
+#define for_each_mem_cgroup(iter)			\
+	for (iter = mem_cgroup_iter(NULL, NULL, NULL);	\
+	     iter != NULL;				\
+	     iter = mem_cgroup_iter(NULL, iter, NULL))
+
+void memcg1_css_offline(struct mem_cgroup *memcg);
+
+/* for encoding cft->private value on file */
+enum res_type {
+	_MEM,
+	_MEMSWAP,
+	_KMEM,
+	_TCP,
+};
+
+bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
+				enum mem_cgroup_events_target target);
+unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap);
+void mem_cgroup_oom_notify(struct mem_cgroup *memcg);
+ssize_t memcg_write_event_control(struct kernfs_open_file *of,
+				  char *buf, size_t nbytes, loff_t off);
+
+
 #endif	/* __MM_MEMCONTROL_V1_H */