From eea86af6b1e18d6fa8dc959e3ddc0100f27aff9f Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Wed, 19 Jun 2013 12:51:20 +0200 Subject: [PATCH] net: sock: adapt SOCK_MIN_RCVBUF and SOCK_MIN_SNDBUF The current situation is that SOCK_MIN_RCVBUF is 2048 + sizeof(struct sk_buff)) while SOCK_MIN_SNDBUF is 2048. Since in both cases, skb->truesize is used for sk_{r,w}mem_alloc accounting, we should have both sizes adjusted via defining a TCP_SKB_MIN_TRUESIZE. Further, as Eric Dumazet points out, the minimal skb truesize in transmit path is SKB_TRUESIZE(2048) after commit f07d960df33c5 ("tcp: avoid frag allocation for small frames"), and tcp_sendmsg() tries to limit skb size to half the congestion window, meaning we try to build two skbs at minimum. Thus, having SOCK_MIN_SNDBUF as 2048 can hit a small regression for some applications setting to low SO_SNDBUF / SO_RCVBUF. Note that we define a TCP_SKB_MIN_TRUESIZE, because SKB_TRUESIZE(2048) adds SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), but in case of TCP skbs, the skb_shared_info is part of the 2048 bytes allocation for skb->head. The minor adaption in sk_stream_moderate_sndbuf() is to silence a warning by using a typed max macro, as similarly done in SOCK_MIN_RCVBUF occurences, that would appear otherwise. Suggested-by: Eric Dumazet Signed-off-by: Daniel Borkmann Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/net/sock.h | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index 21db792bffa5..ea6206ccc896 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -2047,18 +2047,21 @@ static inline void sk_wake_async(struct sock *sk, int how, int band) sock_wake_async(sk->sk_socket, how, band); } -#define SOCK_MIN_SNDBUF 2048 -/* - * Since sk_rmem_alloc sums skb->truesize, even a small frame might need - * sizeof(sk_buff) + MTU + padding, unless net driver perform copybreak +/* Since sk_{r,w}mem_alloc sums skb->truesize, even a small frame might + * need sizeof(sk_buff) + MTU + padding, unless net driver perform copybreak. + * Note: for send buffers, TCP works better if we can build two skbs at + * minimum. */ -#define SOCK_MIN_RCVBUF (2048 + sizeof(struct sk_buff)) +#define TCP_SKB_MIN_TRUESIZE (2048 + sizeof(struct sk_buff)) + +#define SOCK_MIN_SNDBUF (TCP_SKB_MIN_TRUESIZE * 2) +#define SOCK_MIN_RCVBUF TCP_SKB_MIN_TRUESIZE static inline void sk_stream_moderate_sndbuf(struct sock *sk) { if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) { sk->sk_sndbuf = min(sk->sk_sndbuf, sk->sk_wmem_queued >> 1); - sk->sk_sndbuf = max(sk->sk_sndbuf, SOCK_MIN_SNDBUF); + sk->sk_sndbuf = max_t(u32, sk->sk_sndbuf, SOCK_MIN_SNDBUF); } }