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Daniel Borkmann authored
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 f07d960d ("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 <eric.dumazet@gmail.com> Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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