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Date:   Thu, 20 Jan 2022 07:27:36 -0800
From:   Keith Busch <kbusch@kernel.org>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Jason Gunthorpe <jgg@nvidia.com>,
        Matthew Wilcox <willy@infradead.org>,
        linux-kernel@vger.kernel.org,
        Joao Martins <joao.m.martins@oracle.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Ming Lei <ming.lei@redhat.com>, linux-block@vger.kernel.org,
        netdev@vger.kernel.org, linux-mm@kvack.org,
        linux-rdma@vger.kernel.org, dri-devel@lists.freedesktop.org,
        nvdimm@lists.linux.dev
Subject: Re: Phyr Starter
Message-ID: <20220120152736.GB383746@dhcp-10-100-145-180.wdc.com>
References: <YdyKWeU0HTv8m7wD@casper.infradead.org>
 <20220111004126.GJ2328285@nvidia.com>
 <20220120135602.GA11223@lst.de>
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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).