From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH RFC 1/6] skbuff: support per-page destructors in copy_ubufs Date: Fri, 11 May 2012 19:30:58 +0300 Message-ID: <20120511163057.GB10344@redhat.com> References: <8a3235fbceef37758ef23169c4c152e8d1251d3b.1336397823.git.mst@redhat.com> <1336671977.14220.26.camel@zakaz.uk.xensource.com> <20120510184246.GE14647@redhat.com> <1336726800.23818.33.camel@zakaz.uk.xensource.com> <1336733892.23818.69.camel@zakaz.uk.xensource.com> <20120511120836.GA4637@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Miller , "netdev@vger.kernel.org" , "eric.dumazet@gmail.com" To: Ian Campbell Return-path: Received: from mx1.redhat.com ([209.132.183.28]:21123 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932622Ab2EKSaa (ORCPT ); Fri, 11 May 2012 14:30:30 -0400 Content-Disposition: inline In-Reply-To: <20120511120836.GA4637@redhat.com> Sender: netdev-owner@vger.kernel.org List-ID: On Fri, May 11, 2012 at 03:08:36PM +0300, Michael S. Tsirkin wrote: > On Fri, May 11, 2012 at 11:58:12AM +0100, Ian Campbell wrote: > > On Fri, 2012-05-11 at 10:00 +0100, Ian Campbell wrote: > > > I'm seeing copy_ubufs called in my remote NFS test, which I don't > > > think I expected -- I'll investigate why this is happening today. > > > > It's tcp_transmit_skb which can (conditionally) call skb_clone > > (backtrace below) > > Interesting. I didn't realise we clone skbs on data path: > tcp_write_xmit calls tcp_transmit_skb with clone_it flag. > Could someone comment on why we need to clone on good path > like this? Hmm, it's in case we need to retransmit it later. > -- > MST