On Fri, Sep 7, 2018 at 12:03 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> Problem is : we have platforms with more than 100 cpus, and
> sk_memory_allocated() cost will be too expensive,
> especially if the host is under memory pressure, since all cpus will
> touch their private counter.
>
> per cpu variables do not really scale, they were ok 10 years ago when
> no more than 16 cpus were the norm.
>
> I would prefer change TCP to not aggressively call
> __sk_mem_reduce_allocated() from tcp_write_timer()
>
> Ideally only tcp_retransmit_timer() should attempt to reduce forward
> allocations, after recurring timeout.
>
> Note that after 20c64d5cd5a2bdcdc8982a06cb05e5e1bd851a3d ("net: avoid
> sk_forward_alloc overflows")
> we have better control over sockets having huge forward allocations.
>
> Something like :
Or something less risky :
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 7fdf222a0bdfe9775970082f6b5dcdcc82b2ae1a..0aee80b6966cb2898e46350c761f9eb431ff1206
100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -604,7 +604,8 @@ void tcp_write_timer_handler(struct sock *sk)
}
out:
- sk_mem_reclaim(sk);
+ if (tcp_under_memory_pressure(sk))
+ sk_mem_reclaim(sk);
}
static void tcp_write_timer(struct timer_list *t)
