From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Chris Friesen" Subject: Re: seeing strange values for tcp sk_rmem_alloc Date: Tue, 01 Dec 2009 11:28:50 -0600 Message-ID: <4B155252.1040604@nortel.com> References: <4B15416A.2060202@nortel.com> <4B154B29.1030807@cosmosbay.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, Linux kernel To: Eric Dumazet Return-path: Received: from zrtps0kp.nortel.com ([47.140.192.56]:54724 "EHLO zrtps0kp.nortel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753402AbZLARbP (ORCPT ); Tue, 1 Dec 2009 12:31:15 -0500 In-Reply-To: <4B154B29.1030807@cosmosbay.com> Sender: netdev-owner@vger.kernel.org List-ID: On 12/01/2009 10:58 AM, Eric Dumazet wrote: > Me wondering why you think sk_rmem_alloc is about TX side. > Its used in RX path. rmem means ReadMemory. Yep, I realize this. > You can send 1 Gbytes of data, and sk_rmem_alloc doesnt change, if your > TCP stream is unidirectionnal. > > sk_rmem_alloc grows when skb are queued into receive queue > sk_rmem_alloc shrinks when application reads this receive queue. I realize this. I sent the data from a socket to itself. It could just as easily be done with two tcp sockets. The important thing is that I control both the tx and rx sides, so I know how much data should be present in the rx queue at any point in time. The part that surprised me was that I could send multiple chunks of data without sk_rmem_alloc changing on the socket to which the data was being sent. Then it would jump up by a large amount (up to 20K) all at once. I'm starting to suspect that the discrepency might have something to do with the skb_copy_datagram_iovec() call in tcp_data_queue(), and how skb_set_owner_r() is only called if "eaten" is <= 0. This could be totally off-base though. Chris