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

[Dan Williams]

On Fri, Dec 20, 2019 at 4:41 PM John Hubbard <jhubbard@xxxxxxxxxx> 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