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

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Date:   Fri, 20 Dec 2019 16:53:50 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     Jan Kara <jack@...e.cz>, 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>,
        Jérôme Glisse <jglisse@...hat.com>,
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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 4:51 PM, Dan Williams wrote:
> On Fri, Dec 20, 2019 at 4:41 PM John Hubbard <jhubbard@...dia.com> wrote:
>>
>> 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. :)
> 
> You too can have the power of the gods for the low low price of a
> kernel command line parameter, or a qemu setup.
> 
> Details here:
> 
> https://nvdimm.wiki.kernel.org/how_to_choose_the_correct_memmap_kernel_parameter_for_pmem_on_your_system
> https://nvdimm.wiki.kernel.org/pmem_in_qemu
> 

Sweeeet! Now I can really cause some damage. :)

thanks,
-- 
John Hubbard
NVIDIA