Re: Bug: Performance regression in 1013af4f585f: mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race

[David Hildenbrand <david@redhat.com>]

>>>> Why is a tlb_remove_table_sync_one() needed in huge_pmd_unshare()?
>>>
>>> Because nothing else on that path is guaranteed to send any IPIs
>>> before the page table becomes reusable in another process.
>>
>> I feel that David's suggestion of just disallowing the use of shared page
>> tables like this (I mean really does it actually come up that much?) is the
>> right one then.
> 
> Yeah, I also like that suggestion.

I started hacking on this (only found a bit of time this week), and in 
essence, we'll be using the mmu_gather when unsharing to collect the 
pages and handle the TLB flushing etc.

(TLB flushing in that hugetlb area is a mess)

It almost looks like a cleanup.

Having that said, it will take a bit longer to finish it and, of course, 
I first have to test it then to see if it even works.

But it looks doable. :)

-- 
Cheers

David / dhildenb