From 2e12072c67b5f65fc71a569985a1262531fbdc06 Mon Sep 17 00:00:00 2001 From: Abel Wu Date: Thu, 19 Oct 2023 20:00:25 +0800 Subject: sock: Doc behaviors for pressure heurisitics There are now two accounting infrastructures for skmem, while the heuristics in __sk_mem_raise_allocated() were actually introduced before memcg was born. Add some comments to clarify whether they can be applied to both infrastructures or not. Suggested-by: Shakeel Butt Signed-off-by: Abel Wu Acked-by: Shakeel Butt Reviewed-by: Simon Horman Link: https://lore.kernel.org/r/20231019120026.42215-2-wuyun.abel@bytedance.com Signed-off-by: Paolo Abeni --- net/core/sock.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'net/core') diff --git a/net/core/sock.c b/net/core/sock.c index 43842520db86..9f969e3c2ddf 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -3067,7 +3067,14 @@ int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind) if (allocated > sk_prot_mem_limits(sk, 2)) goto suppress_allocation; - /* guarantee minimum buffer size under pressure */ + /* Guarantee minimum buffer size under pressure (either global + * or memcg) to make sure features described in RFC 7323 (TCP + * Extensions for High Performance) work properly. + * + * This rule does NOT stand when exceeds global or memcg's hard + * limit, or else a DoS attack can be taken place by spawning + * lots of sockets whose usage are under minimum buffer size. + */ if (kind == SK_MEM_RECV) { if (atomic_read(&sk->sk_rmem_alloc) < sk_get_rmem0(sk, prot)) return 1; @@ -3088,6 +3095,11 @@ int __sk_mem_raise_allocated(struct sock *sk, int size, int amt, int kind) if (!sk_under_memory_pressure(sk)) return 1; + + /* Try to be fair among all the sockets under global + * pressure by allowing the ones that below average + * usage to raise. + */ alloc = sk_sockets_allocated_read_positive(sk); if (sk_prot_mem_limits(sk, 2) > alloc * sk_mem_pages(sk->sk_wmem_queued + -- cgit v1.2.3