Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb)

[David Hildenbrand]

On 18.12.21 03:42, Linus Torvalds wrote:
> On Fri, Dec 17, 2021 at 6:17 PM Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>>
>> I think the hugepage code should use the exact same logic that the
>> regular wp fault code does.
> 
> IOW, I think that this stupid (AND UNTESTED) patch should likely just
> fix David's test-case with the hugepage and splice thing..
> 
> Or at least be somewhat close.  But it should be paired with the GUP
> side doing the right thing too, of course. Maybe it already does,
> maybe it doesn't, I didn't check...
> 
> And maybe there's something subtle about the page_count() of a THP
> entry. Again, I can't really claim to have tested this all, but I'm
> hoping this makes somebody go "Ahh, now I see what Linus means"

Not the reaction you are hoping for: "Gah, Linus still doesn't see why
the page_count is just wrong". :)

See the mail I just wrote, let's get a common understanding of how our
check should actually look like.

-- 
Thanks,

David / dhildenb