From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH net,v2] net: sock: adapt SOCK_MIN_RCVBUF and SOCK_MIN_SNDBUF Date: Wed, 19 Jun 2013 05:19:15 -0700 Message-ID: <1371644355.3252.307.camel@edumazet-glaptop> References: <1371639080-10699-1-git-send-email-dborkman@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, netdev@vger.kernel.org To: Daniel Borkmann Return-path: Received: from mail-ee0-f42.google.com ([74.125.83.42]:34675 "EHLO mail-ee0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934108Ab3FSMTU (ORCPT ); Wed, 19 Jun 2013 08:19:20 -0400 Received: by mail-ee0-f42.google.com with SMTP id c4so3177110eek.29 for ; Wed, 19 Jun 2013 05:19:18 -0700 (PDT) In-Reply-To: <1371639080-10699-1-git-send-email-dborkman@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 2013-06-19 at 12:51 +0200, Daniel Borkmann wrote: > 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 > --- > v1 -> v2: > - Applied Eric's feedback, fixed up commit message > - Set subject to 'net' instead of 'net-next' due to the reported regression I am fine with this patch (I already run it as a matter of fact), but I think its net-next material : Regression is not new, and concerns very pathological cases, where applications relied on some non documented behavior of network stack. Signed-off-by: Eric Dumazet