linux-kernel - Re: [RFC PATCH 00/28] Removing struct page from P2PDMA

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Message-ID: <20190624181632.GC8268@ziepe.ca>
Date:   Mon, 24 Jun 2019 15:16:32 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-pci@...r.kernel.org, linux-rdma <linux-rdma@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Keith Busch <kbusch@...nel.org>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [RFC PATCH 00/28] Removing struct page from P2PDMA

On Mon, Jun 24, 2019 at 10:53:38AM -0600, Logan Gunthorpe wrote:
> > It is only a very narrow case where you can take shortcuts with
> > dma_addr_t, and I don't think shortcuts like are are appropriate for
> > the mainline kernel..
> 
> I don't think it's that narrow and it opens up a lot of avenues for
> system design that people are wanting to go. If your high speed data
> path can avoid the root complex and CPU, you can design a system which a
> much smaller CPU and fewer lanes directed at the CPU.

I mean the shortcut that something generates dma_addr_t for Device A
and then passes it to Device B - that is too hacky for mainline.

Sounded like this series does generate the dma_addr for the correct
device..

Jason