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authorEric Dumazet <edumazet@google.com>2020-09-30 15:54:57 +0300
committerDavid S. Miller <davem@davemloft.net>2020-10-01 00:21:30 +0300
commita37c2134bed6f28c6d6aefa2699331e6e4e9c4f1 (patch)
treef1ce9d23e66fd51f5efcd7ea38663db68f27d5ca /net/ipv4/tcp_output.c
parentb6b6d6533a14b5ddcf9f9c5239fc3721fc6beda0 (diff)
downloadlinux-a37c2134bed6f28c6d6aefa2699331e6e4e9c4f1.tar.xz
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>
Diffstat (limited to 'net/ipv4/tcp_output.c')
-rw-r--r--net/ipv4/tcp_output.c11
1 files changed, 8 insertions, 3 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 6bd4e383030e..bf48cd73e967 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;
}