netdev - RE: [PATCH v3 net-next 08/14] mlx4: use order-0 pages for RX

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Date:   Tue, 14 Feb 2017 17:17:22 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'David Miller' <davem@...emloft.net>,
        "ttoukan.linux@...il.com" <ttoukan.linux@...il.com>
CC:     "edumazet@...gle.com" <edumazet@...gle.com>,
        "brouer@...hat.com" <brouer@...hat.com>,
        "alexander.duyck@...il.com" <alexander.duyck@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "tariqt@...lanox.com" <tariqt@...lanox.com>,
        "kafai@...com" <kafai@...com>,
        "saeedm@...lanox.com" <saeedm@...lanox.com>,
        "willemb@...gle.com" <willemb@...gle.com>,
        "bblanco@...mgrid.com" <bblanco@...mgrid.com>,
        "ast@...nel.org" <ast@...nel.org>,
        "eric.dumazet@...il.com" <eric.dumazet@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: RE: [PATCH v3 net-next 08/14] mlx4: use order-0 pages for RX

From: David Miller
> Sent: 14 February 2017 17:04
...
> One path I see around all of this is full integration.  Meaning that
> we can free pages into the page allocator which are still DMA mapped.
> And future allocations from that device are prioritized to take still
> DMA mapped objects.
...

For systems with 'expensive' iommu has anyone tried separating the
allocation of iommu resource (eg page table slots) from their
assignment to physical pages?

Provided the page sizes all match, setting up a receive buffer might
be as simple as writing the physical address into the iommu slot
that matches the ring entry.

Or am I thinking about hardware that is much simpler than real life?

	David