Merge branch 'net-reduce-tcp_memory_allocated-inflation'

Eric Dumazet says:

====================
net: reduce tcp_memory_allocated inflation

Hosts with a lot of sockets tend to hit so called TCP memory pressure,
leading to very bad TCP performance and/or OOM.

The problem is that some TCP sockets can hold up to 2MB of 'forward
allocations' in their per-socket cache (sk->sk_forward_alloc),
and there is no mechanism to make them relinquish their share
under mem pressure.
Only under some potentially rare events their share is reclaimed,
one socket at a time.

In this series, I implemented a per-cpu cache instead of a per-socket one.

Each CPU has a +1/-1 MB (256 pages on x86) forward alloc cache, in order
to not dirty tcp_memory_allocated shared cache line too often.

We keep sk->sk_forward_alloc values as small as possible, to meet
memcg page granularity constraint.

Note that memcg already has a per-cpu cache, although MEMCG_CHARGE_BATCH
is defined to 32 pages, which seems a bit small.

Note that while this cover letter mentions TCP, this work is generic
and supports TCP, UDP, DECNET, SCTP.
====================

Link: https://lore.kernel.org/r/20220609063412.2205738-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 4 insertions, 9 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9984d23a7f3e..14ebb4ec4a51 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -294,6 +294,8 @@ EXPORT_SYMBOL(sysctl_tcp_mem);
 
 atomic_long_t tcp_memory_allocated ____cacheline_aligned_in_smp;	/* Current allocated memory. */
 EXPORT_SYMBOL(tcp_memory_allocated);
+DEFINE_PER_CPU(int, tcp_memory_per_cpu_fw_alloc);
+EXPORT_PER_CPU_SYMBOL_GPL(tcp_memory_per_cpu_fw_alloc);
 
 #if IS_ENABLED(CONFIG_SMC)
 DEFINE_STATIC_KEY_FALSE(tcp_have_smc);
@@ -856,9 +858,6 @@ struct sk_buff *tcp_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp,
 {
 	struct sk_buff *skb;
 
-	if (unlikely(tcp_under_memory_pressure(sk)))
-		sk_mem_reclaim_partial(sk);
-
 	skb = alloc_skb_fclone(size + MAX_TCP_HEADER, gfp);
 	if (likely(skb)) {
 		bool mem_scheduled;
@@ -2762,8 +2761,6 @@ void __tcp_close(struct sock *sk, long timeout)
 		__kfree_skb(skb);
 	}
 
-	sk_mem_reclaim(sk);
-
 	/* If socket has been already reset (e.g. in tcp_reset()) - kill it. */
 	if (sk->sk_state == TCP_CLOSE)
 		goto adjudge_to_death;
@@ -2871,7 +2868,6 @@ adjudge_to_death:
 		}
 	}
 	if (sk->sk_state != TCP_CLOSE) {
-		sk_mem_reclaim(sk);
 		if (tcp_check_oom(sk, 0)) {
 			tcp_set_state(sk, TCP_CLOSE);
 			tcp_send_active_reset(sk, GFP_ATOMIC);
@@ -2949,7 +2945,6 @@ void tcp_write_queue_purge(struct sock *sk)
 	}
 	tcp_rtx_queue_purge(sk);
 	INIT_LIST_HEAD(&tcp_sk(sk)->tsorted_sent_queue);
-	sk_mem_reclaim(sk);
 	tcp_clear_all_retrans_hints(tcp_sk(sk));
 	tcp_sk(sk)->packets_out = 0;
 	inet_csk(sk)->icsk_backoff = 0;
@@ -4661,11 +4656,11 @@ void __init tcp_init(void)
 	max_wshare = min(4UL*1024*1024, limit);
 	max_rshare = min(6UL*1024*1024, limit);
 
-	init_net.ipv4.sysctl_tcp_wmem[0] = SK_MEM_QUANTUM;
+	init_net.ipv4.sysctl_tcp_wmem[0] = PAGE_SIZE;
 	init_net.ipv4.sysctl_tcp_wmem[1] = 16*1024;
 	init_net.ipv4.sysctl_tcp_wmem[2] = max(64*1024, max_wshare);
 
-	init_net.ipv4.sysctl_tcp_rmem[0] = SK_MEM_QUANTUM;
+	init_net.ipv4.sysctl_tcp_rmem[0] = PAGE_SIZE;
 	init_net.ipv4.sysctl_tcp_rmem[1] = 131072;
 	init_net.ipv4.sysctl_tcp_rmem[2] = max(131072, max_rshare);