net: tcp_memcontrol: simplify the per-memcg limit access

tcp_memcontrol replicates the global sysctl_mem limit array per cgroup,
but it only ever sets these entries to the value of the memory_allocated
page_counter limit.  Use the latter directly.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Vladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/memcontrol.h

@@ -89,7 +89,6 @@ struct cg_proto {
 	struct page_counter	memory_allocated;	/* Current allocated memory. */
 	int			memory_pressure;
 	bool			active;
-	long			sysctl_mem[3];
 	/*
 	 * memcg field is used to find which memcg we belong directly
 	 * Each memcg struct can hold more than one cg_proto, so container_of

include/net/sock.h

@@ -1162,10 +1162,12 @@ static inline void sk_enter_memory_pressure(struct sock *sk)
 
 static inline long sk_prot_mem_limits(const struct sock *sk, int index)
 {
-	long *prot = sk->sk_prot->sysctl_mem;
+	long limit = sk->sk_prot->sysctl_mem[index];
+
 	if (mem_cgroup_sockets_enabled && sk->sk_cgrp)
-		prot = sk->sk_cgrp->sysctl_mem;
-	return prot[index];
+		limit = min_t(long, limit, sk->sk_cgrp->memory_allocated.limit);
+
+	return limit;
 }
 
 static inline void memcg_memory_allocated_add(struct cg_proto *prot,

net/ipv4/tcp_memcontrol.c

@@ -21,9 +21,6 @@ int tcp_init_cgroup(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
 	if (!cg_proto)
 		return 0;
 
-	cg_proto->sysctl_mem[0] = sysctl_tcp_mem[0];
-	cg_proto->sysctl_mem[1] = sysctl_tcp_mem[1];
-	cg_proto->sysctl_mem[2] = sysctl_tcp_mem[2];
 	cg_proto->memory_pressure = 0;
 	cg_proto->memcg = memcg;
 
@@ -54,7 +51,6 @@ EXPORT_SYMBOL(tcp_destroy_cgroup);
 static int tcp_update_limit(struct mem_cgroup *memcg, unsigned long nr_pages)
 {
 	struct cg_proto *cg_proto;
-	int i;
 	int ret;
 
 	cg_proto = tcp_prot.proto_cgroup(memcg);
@@ -65,10 +61,6 @@ static int tcp_update_limit(struct mem_cgroup *memcg, unsigned long nr_pages)
 	if (ret)
 		return ret;
 
-	for (i = 0; i < 3; i++)
-		cg_proto->sysctl_mem[i] = min_t(long, nr_pages,
-						sysctl_tcp_mem[i]);
-
 	if (!cg_proto->active) {
 		/*
 		 * The active flag needs to be written after the static_key