[PATCH v5 3/9] mm/mremap: Use pmd/pud_poplulate to update page table entries

[Aneesh Kumar K.V]

On 5/20/21 6:16 PM, Peter Xu wrote:
> On Thu, May 20, 2021 at 01:56:54PM +0530, Aneesh Kumar K.V wrote:
>>> This seems to work at least for my userfaultfd test on shmem, however I don't
>>> fully understand the commit message [1] on: How do we guarantee we're not
>>> moving a thp pte?
>>>
>>
>> move_page_tables() checks for pmd_trans_huge() and ends up calling
>> move_huge_pmd if it is a THP entry.
> 
> Sorry to be unclear: what if a huge pud thp?
> 

I am still checking. Looking at the code before commit 
c49dd340180260c6239e453263a9a244da9a7c85, I don't see kernel handling 
huge pud thp. I haven't studied huge pud thp enough to understand 
whether c49dd340180260c6239e453263a9a244da9a7c85 intent to add that 
support.

We can do a move_huge_pud() like we do for huge pmd thp. But I am not 
sure whether we handle those VMA's earlier and restrict mremap on them?

Are huge pud thp only allowed with DAX vmas?


-aneesh