linux-kernel - Re: [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL

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Message-ID: <437f2bff-13ba-0ae9-2f3c-bc8eb82d20f0@nvidia.com>
Date:   Fri, 20 Dec 2019 16:41:35 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Dan Williams <dan.j.williams@...el.com>, Jan Kara <jack@...e.cz>
CC:     Leon Romanovsky <leon@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Alex Williamson" <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
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        Maor Gottlieb <maorg@...lanox.com>
Subject: Re: [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL_PIN

On 12/20/19 4:33 PM, Dan Williams wrote:
...
>> I believe there might be also a different solution for this: For
>> transparent huge pages, we could find a space in 'struct page' of the
>> second page in the huge page for proper pin counter and just account pins
>> there so we'd have full width of 32-bits for it.
> 
> That would require THP accounting for dax pages. It is something that
> was probably going to be needed, but this would seem to force the
> issue.
> 

Thanks for mentioning that, it wasn't obvious to me yet. 

How easy is it for mere mortals outside of Intel, to set up a DAX (nvdimm?)
test setup? I'd hate to go into this without having that coverage up
and running. It's been sketchy enough as it is. :)

thanks,
-- 
John Hubbard
NVIDIA