netdev - Re: Phyr Starter

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Message-ID: <20220120152736.GB383746@dhcp-10-100-145-180.wdc.com>
Date:   Thu, 20 Jan 2022 07:27:36 -0800
From:   Keith Busch <kbusch@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        linux-kernel@...r.kernel.org,
        Joao Martins <joao.m.martins@...cle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Ming Lei <ming.lei@...hat.com>, linux-block@...r.kernel.org,
        netdev@...r.kernel.org, linux-mm@...ck.org,
        linux-rdma@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        nvdimm@...ts.linux.dev
Subject: Re: Phyr Starter

On Thu, Jan 20, 2022 at 02:56:02PM +0100, Christoph Hellwig wrote:
>  - on the input side to dma mapping the bio_vecs (or phyrs) are chained
>    as bios or whatever the containing structure is.  These already exist
>    and have infrastructure at least in the block layer
>  - on the output side I plan for two options:
> 
> 	1) we have a sane IOMMU and everyting will be coalesced into a
> 	   single dma_range.  This requires setting the block layer
> 	   merge boundary to match the IOMMU page size, but that is
> 	   a very good thing to do anyway.

It doesn't look like IOMMU page sizes are exported, or even necessarily
consistently sized on at least one arch (power).