mm: memcg: factor out legacy socket memory accounting code

Move out the legacy cgroup v1 socket memory accounting code into
mm/memcontrol-v1.c.

This commit introduces three new functions: memcg1_tcpmem_active(),
memcg1_charge_skmem() and memcg1_uncharge_skmem(), which contain all
cgroup v1-specific code and become trivial if CONFIG_MEMCG_V1 isn't set.

Note, that !!memcg->tcpmem_pressure check in
mem_cgroup_under_socket_pressure() can't be easily moved into
memcontrol-v1.h without including memcontrol-v1.h from memcontrol.h which
isn't a good idea, so it's better to just #ifdef it.

Link: https://lkml.kernel.org/r/20240628210317.272856-3-roman.gushchin@linux.devSigned-off-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/memcontrol.h

@@ -1650,8 +1650,10 @@ void mem_cgroup_sk_alloc(struct sock *sk);
 void mem_cgroup_sk_free(struct sock *sk);
 static inline bool mem_cgroup_under_socket_pressure(struct mem_cgroup *memcg)
 {
+#ifdef CONFIG_MEMCG_V1
 	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
 		return !!memcg->tcpmem_pressure;
+#endif /* CONFIG_MEMCG_V1 */
 	do {
 		if (time_before(jiffies, READ_ONCE(memcg->socket_pressure)))
 			return true;

mm/memcontrol-v1.c

@@ -2925,6 +2925,23 @@ void memcg1_account_kmem(struct mem_cgroup *memcg, int nr_pages)
 }
 #endif /* CONFIG_MEMCG_KMEM */
 
+bool memcg1_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,
+			 gfp_t gfp_mask)
+{
+	struct page_counter *fail;
+
+	if (page_counter_try_charge(&memcg->tcpmem, nr_pages, &fail)) {
+		memcg->tcpmem_pressure = 0;
+		return true;
+	}
+	memcg->tcpmem_pressure = 1;
+	if (gfp_mask & __GFP_NOFAIL) {
+		page_counter_charge(&memcg->tcpmem, nr_pages);
+		return true;
+	}
+	return false;
+}
+
 static int __init memcg1_init(void)
 {
 	int node;

mm/memcontrol-v1.h

@@ -103,6 +103,17 @@ void memcg1_check_events(struct mem_cgroup *memcg, int nid);
 void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s);
 
 void memcg1_account_kmem(struct mem_cgroup *memcg, int nr_pages);
+static inline bool memcg1_tcpmem_active(struct mem_cgroup *memcg)
+{
+	return memcg->tcpmem_active;
+}
+bool memcg1_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,
+			 gfp_t gfp_mask);
+static inline void memcg1_uncharge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
+{
+	page_counter_uncharge(&memcg->tcpmem, nr_pages);
+}
+
 extern struct cftype memsw_files[];
 extern struct cftype mem_cgroup_legacy_files[];
 
@@ -122,6 +133,11 @@ static inline void memcg1_check_events(struct mem_cgroup *memcg, int nid) {}
 static inline void memcg1_stat_format(struct mem_cgroup *memcg, struct seq_buf *s) {}
 
 static inline void memcg1_account_kmem(struct mem_cgroup *memcg, int nr_pages) {}
+static inline bool memcg1_tcpmem_active(struct mem_cgroup *memcg) { return false; }
+static inline bool memcg1_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,
+				       gfp_t gfp_mask) { return true; }
+static inline void memcg1_uncharge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages) {}
+
 extern struct cftype memsw_files[];
 extern struct cftype mem_cgroup_legacy_files[];
 #endif	/* CONFIG_MEMCG_V1 */

mm/memcontrol.c

@@ -3753,7 +3753,7 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
 	if (cgroup_subsys_on_dfl(memory_cgrp_subsys) && !cgroup_memory_nosocket)
 		static_branch_dec(&memcg_sockets_enabled_key);
 
-	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && memcg->tcpmem_active)
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && memcg1_tcpmem_active(memcg))
 		static_branch_dec(&memcg_sockets_enabled_key);
 
 #if defined(CONFIG_MEMCG_KMEM)
@@ -4979,7 +4979,7 @@ void mem_cgroup_sk_alloc(struct sock *sk)
 	memcg = mem_cgroup_from_task(current);
 	if (mem_cgroup_is_root(memcg))
 		goto out;
-	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && !memcg->tcpmem_active)
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && !memcg1_tcpmem_active(memcg))
 		goto out;
 	if (css_tryget(&memcg->css))
 		sk->sk_memcg = memcg;
@@ -5005,20 +5005,8 @@ void mem_cgroup_sk_free(struct sock *sk)
 bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,
 			     gfp_t gfp_mask)
 {
-	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
-		struct page_counter *fail;
-
-		if (page_counter_try_charge(&memcg->tcpmem, nr_pages, &fail)) {
-			memcg->tcpmem_pressure = 0;
-			return true;
-		}
-		memcg->tcpmem_pressure = 1;
-		if (gfp_mask & __GFP_NOFAIL) {
-			page_counter_charge(&memcg->tcpmem, nr_pages);
-			return true;
-		}
-		return false;
-	}
+	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return memcg1_charge_skmem(memcg, nr_pages, gfp_mask);
 
 	if (try_charge(memcg, gfp_mask, nr_pages) == 0) {
 		mod_memcg_state(memcg, MEMCG_SOCK, nr_pages);
@@ -5036,7 +5024,7 @@ bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages,
 void mem_cgroup_uncharge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
 {
 	if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
-		page_counter_uncharge(&memcg->tcpmem, nr_pages);
+		memcg1_uncharge_skmem(memcg, nr_pages);
 		return;
 	}