From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net,v2] net: sock: adapt SOCK_MIN_RCVBUF and SOCK_MIN_SNDBUF Date: Wed, 19 Jun 2013 21:17:21 -0700 (PDT) Message-ID: <20130619.211721.1594350084165223337.davem@davemloft.net> References: <1371639080-10699-1-git-send-email-dborkman@redhat.com> <1371644355.3252.307.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: dborkman@redhat.com, netdev@vger.kernel.org To: eric.dumazet@gmail.com Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:48594 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751092Ab3FTERW (ORCPT ); Thu, 20 Jun 2013 00:17:22 -0400 In-Reply-To: <1371644355.3252.307.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet Date: Wed, 19 Jun 2013 05:19:15 -0700 > 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 Applied, thanks guys.