netdev - Re: [Lsf] [Lsf-pc] [LSF/MM TOPIC] Generic page-pool recycle facility?

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Date:	Mon, 11 Apr 2016 11:53:10 -0700
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>,
	Thadeu Lima de Souza Cascardo <cascardo@...hat.com>
CC:	"lsf@...ts.linux-foundation.org" <lsf@...ts.linux-foundation.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Brenden Blanco <bblanco@...mgrid.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-mm <linux-mm@...ck.org>, "Mel Gorman" <mgorman@...e.de>,
	Tom Herbert <tom@...bertland.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	"lsf-pc@...ts.linux-foundation.org" 
	<lsf-pc@...ts.linux-foundation.org>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [Lsf] [Lsf-pc] [LSF/MM TOPIC] Generic page-pool recycle facility?

On 04/11/2016 11:37 AM, Jesper Dangaard Brouer wrote:
> On Mon, 11 Apr 2016 14:46:25 -0300
> Thadeu Lima de Souza Cascardo <cascardo@...hat.com> wrote:
>
>> So, Jesper, please take into consideration that this pool design
>> would rather be per device. Otherwise, we allow some device to write
>> into another's device/driver memory.
>
> Yes, that was my intended use.  I want to have a page-pool per device.
> I actually, want to go as far as a page-pool per NIC HW RX-ring queue.
>
> Because the other use-case for the page-pool is zero-copy RX.
>
> The NIC HW trick is that we today can create a HW filter in the NIC
> (via ethtool) and place that traffic into a separate RX queue in the
> NIC.  Lets say matching NFS traffic or guest traffic. Then we can allow
> RX zero-copy of these pages, into the application/guest, somehow
> binding it to RX queue, e.g. introducing a "cross-domain-id" in the
> page-pool page that need to match.

I think it is important to keep in mind that using a page pool for 
zero-copy RX is specific to protocols that are based on TCP/IP. 
Protocols like FC, SRP and iSER have been designed such that the side 
that allocates the buffers also initiates the data transfer (the target 
side). With TCP/IP however transferring data and allocating receive 
buffers happens by opposite sides of the connection.

Bart.