[TCP]: Do not purge sk_forward_alloc entirely in tcp_delack_timer().

Otherwise we beat heavily on the global tcp_memory atomics
when all of the sockets in the system are slowly sending
perioding packet clumps.

Noticed and suggested by Eric Dumazet.

Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 9 insertions, 1 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index 786fae858e77..902324488d0f 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -759,6 +759,14 @@ static inline void sk_mem_reclaim(struct sock *sk)
                 __sk_mem_reclaim(sk);
 }
 
+static inline void sk_mem_reclaim_partial(struct sock *sk)
+{
+        if (!sk_has_account(sk))
+                return;
+        if (sk->sk_forward_alloc > SK_MEM_QUANTUM)
+                __sk_mem_reclaim(sk);
+}
+
 static inline void sk_mem_charge(struct sock *sk, int size)
 {
         if (!sk_has_account(sk))
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 17931be6d584..803d758a2b12 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -186,7 +186,7 @@ static void tcp_delack_timer(unsigned long data)
                 goto out_unlock;
         }
 
-        sk_mem_reclaim(sk);
+        sk_mem_reclaim_partial(sk);
 
         if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
                 goto out;