netdev - [PATCH net-next] tcp: sk_forced_mem

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Date:   Fri, 10 Jun 2022 20:30:16 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Soheil Hassas Yeganeh <soheil@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next] tcp: sk_forced_mem_schedule() optimization

From: Eric Dumazet <edumazet@...gle.com>

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@...gle.com>
---
 include/net/sock.h | 3 +--
 net/core/sock.c    | 9 ++++++---
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 0063e8410a4e3ed91aef9cf34eb1127f7ce33b93..304a5e39d41e27105148058066e8fa23490cf9fa 100644
--- a/include/net/sock.h
+++ b/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
diff --git a/net/core/sock.c b/net/core/sock.c
index 697d5c8e2f0def49351a7d38ec59ab5e875d3b10..92a0296ccb1842f11fb8dd4b2f768885d05daa8f 100644
--- a/net/core/sock.c
+++ b/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())))
-- 
2.36.1.476.g0c4daa206d-goog