From owner-freebsd-hackers@FreeBSD.ORG Wed Feb 6 16:38:14 2013 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.FreeBSD.org [8.8.178.115]) by hub.freebsd.org (Postfix) with ESMTP id 3DC6133B for ; Wed, 6 Feb 2013 16:38:14 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from bigwig.baldwin.cx (bigknife-pt.tunnel.tserv9.chi1.ipv6.he.net [IPv6:2001:470:1f10:75::2]) by mx1.freebsd.org (Postfix) with ESMTP id 142437E7 for ; Wed, 6 Feb 2013 16:38:14 +0000 (UTC) Received: from pakbsde14.localnet (unknown [38.105.238.108]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id 7EDF1B915; Wed, 6 Feb 2013 11:38:13 -0500 (EST) From: John Baldwin To: Jacques Fourie Subject: Re: Mbuf memory handling Date: Wed, 6 Feb 2013 11:37:35 -0500 User-Agent: KMail/1.13.5 (FreeBSD/8.2-CBSD-20110714-p22; KDE/4.5.5; amd64; ; ) References: <175CCF5F49938B4D99B2E3EF7F558EBE1C73F401F3@SC-VEXCH4.marvell.com> <201302060836.55404.jhb@freebsd.org> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-15" Content-Transfer-Encoding: 7bit Message-Id: <201302061137.35651.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Wed, 06 Feb 2013 11:38:13 -0500 (EST) Cc: Hackers freeBSD , Axel Fischer , Lino Sanfilippo , Markus Althoff X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 06 Feb 2013 16:38:14 -0000 On Wednesday, February 06, 2013 10:20:50 am Jacques Fourie wrote: > On Wed, Feb 6, 2013 at 3:36 PM, John Baldwin wrote: > > > On Wednesday, February 06, 2013 4:50:39 am Lino Sanfilippo wrote: > > > > > > Hi all, > > > > > > I want to implement a device driver for a NIC which stores received data > > into chunks within > > > a page (>=4k) in host memory. One page shall be used for multiple > > packets and freed > > > after all mbufs linked to that page have been processed. So I would like > > to know what is the recommended way > > > to handle this in FreeBSD? Any hints are very appreciated. > > > > I think you can get what you want by allocating M_JUMBOP mbuf clusters for > > your receive buffers. When you want to split out a packet, allocate a new > > packet header mbuf and use m_split() to let it take over the rest of the 4k > > buffer and pass the original mbuf up to if_input() as the new packet. The > > new mbufs you attach to the cluster via m_split() will all hold a reference > > on the backing cluster and it won't be freed until all the mbufs are freed. > > > > The resulting mbufs will not be writeable (M_WRITABLE() will evaluate to > 0), right? I don't know if this will be an issue in this particular > application. No, they only propagate an existing M_RDONLY flag: n->m_flags |= m->m_flags & M_RDONLY; If the first mbuf is writable the splits remain writable from my reading of the code. OTOH, I think in this case read-only buffers passed up to the stack are probably fine since they are already contiguous so any pullup should be a NOP, etc. -- John Baldwin