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

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Date:	Mon, 11 Apr 2016 23:41:57 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Sagi Grimberg <sagi@...mberg.me>
Cc:	Bart Van Assche <bart.vanassche@...disk.com>,
	Christoph Hellwig <hch@...radead.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Tom Herbert <tom@...bertland.com>,
	Brenden Blanco <bblanco@...mgrid.com>,
	"lsf@...ts.linux-foundation.org" <lsf@...ts.linux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"lsf-pc@...ts.linux-foundation.org" 
	<lsf-pc@...ts.linux-foundation.org>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	brouer@...hat.com
Subject: Re: [Lsf] [Lsf-pc] [LSF/MM TOPIC] Generic page-pool recycle
 facility?


On Sun, 10 Apr 2016 21:45:47 +0300 Sagi Grimberg <sagi@...mberg.me> wrote:

> >> This is also very interesting for storage targets, which face the same
> >> issue.  SCST has a mode where it caches some fully constructed SGLs,
> >> which is probably very similar to what NICs want to do.  
> >
> > I think a cached allocator for page sets + the scatterlists that
> > describe these page sets would not only be useful for SCSI target
> > implementations but also for the Linux SCSI initiator. Today the scsi-mq
> > code reserves space in each scsi_cmnd for a scatterlist of
> > SCSI_MAX_SG_SEGMENTS. If scatterlists would be cached together with page
> > sets less memory would be needed per scsi_cmnd.  
> 
> If we go down this road how about also attaching some driver opaques
> to the page sets?

That was the ultimate plan... to leave some opaques bytes left in the
page struct that drivers could use.

In struct page I would need a pointer back to my page_pool struct and a
page flag.  Then, I would need room to store the dma_unmap address.
(And then some of the usual fields are still needed, like the refcnt,
and reusing some of the list constructs).  And a zero-copy cross-domain
id.


For my packet-page idea, I would need a packet length and an offset
where data starts (I can derive the "head-room" for encap from these
two).

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer