tcp: sk_forced_mem_schedule() optimization

sk_memory_allocated_add() has three callers, and returns
to them @memory_allocated.

sk_forced_mem_schedule() is one of them, and ignores
the returned value.

Change sk_memory_allocated_add() to return void.

Change sock_reserve_memory() and __sk_mem_raise_allocated()
to call sk_memory_allocated().

This removes one cache line miss [1] for RPC workloads,
as first skbs in TCP write queue and receive queue go through
sk_forced_mem_schedule().

[1] Cache line holding tcp_memory_allocated.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -1412,7 +1412,7 @@ sk_memory_allocated(const struct sock *sk)
 /* 1 MB per cpu, in page units */
 #define SK_MEMORY_PCPU_RESERVE (1 << (20 - PAGE_SHIFT))
 
-static inline long
+static inline void
 sk_memory_allocated_add(struct sock *sk, int amt)
 {
 	int local_reserve;
@@ -1424,7 +1424,6 @@ sk_memory_allocated_add(struct sock *sk, int amt)
 		atomic_long_add(local_reserve, sk->sk_prot->memory_allocated);
 	}
 	preempt_enable();
-	return sk_memory_allocated(sk);
 }
 
 static inline void

net/core/sock.c

@@ -1019,7 +1019,8 @@ static int sock_reserve_memory(struct sock *sk, int bytes)
 		return -ENOMEM;
 
 	/* pre-charge to forward_alloc */
-	allocated = sk_memory_allocated_add(sk, pages);
+	sk_memory_allocated_add(sk, pages);
+	allocated = sk_memory_allocated(sk);
 	/* If the system goes into memory pressure with this
 	 * precharge, give up and return error.
 	 */
@@ -2906,11 +2907,13 @@ EXPORT_SYMBOL(sk_wait_data);
  */
 int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind)
 {
-	struct proto *prot = sk->sk_prot;
-	long allocated = sk_memory_allocated_add(sk, amt);
 	bool memcg_charge = mem_cgroup_sockets_enabled && sk->sk_memcg;
+	struct proto *prot = sk->sk_prot;
 	bool charged = true;
+	long allocated;
 
+	sk_memory_allocated_add(sk, amt);
+	allocated = sk_memory_allocated(sk);
 	if (memcg_charge &&
 	    !(charged = mem_cgroup_charge_skmem(sk->sk_memcg, amt,
 						gfp_memcg_charge())))