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Subject: Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM
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From:   John Hubbard <jhubbard@nvidia.com>
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On 11/5/20 4:49 AM, Jason Gunthorpe wrote:
> On Thu, Nov 05, 2020 at 10:25:24AM +0100, Daniel Vetter wrote:
>>> /*
>>>   * If we can't determine whether or not a pte is special, then fail immediately
>>>   * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
>>>   * to be special.
>>>   *
>>>   * For a futex to be placed on a THP tail page, get_futex_key requires a
>>>   * get_user_pages_fast_only implementation that can pin pages. Thus it's still
>>>   * useful to have gup_huge_pmd even if we can't operate on ptes.
>>>   */
>>
>> We support hugepage faults in gpu drivers since recently, and I'm not
>> seeing a pud_mkhugespecial anywhere. So not sure this works, but probably
>> just me missing something again.
> 
> It means ioremap can't create an IO page PUD, it has to be broken up.
> 
> Does ioremap even create anything larger than PTEs?
> 

 From my reading, yes. See ioremap_try_huge_pmd().

thanks,
-- 
John Hubbard
NVIDIA