tcp: add exponential backoff in __tcp_send_ack()
Whenever host is under very high memory pressure,
__tcp_send_ack() skb allocation fails, and we setup
a 200 ms (TCP_DELACK_MAX) timer before retrying.
On hosts with high number of TCP sockets, we can spend
considerable amount of cpu cycles in these attempts,
add high pressure on various spinlocks in mm-layer,
ultimately blocking threads attempting to free space
from making any progress.
This patch adds standard exponential backoff to avoid
adding fuel to the fire.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 6bd4e38..bf48cd7 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3941,10 +3941,15 @@ void __tcp_send_ack(struct sock *sk, u32 rcv_nxt)
buff = alloc_skb(MAX_TCP_HEADER,
sk_gfp_mask(sk, GFP_ATOMIC | __GFP_NOWARN));
if (unlikely(!buff)) {
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ unsigned long delay;
+
+ delay = TCP_DELACK_MAX << icsk->icsk_ack.retry;
+ if (delay < TCP_RTO_MAX)
+ icsk->icsk_ack.retry++;
inet_csk_schedule_ack(sk);
- inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
- inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
- TCP_DELACK_MAX, TCP_RTO_MAX);
+ icsk->icsk_ack.ato = TCP_ATO_MIN;
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, delay, TCP_RTO_MAX);
return;
}