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

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Wed, Oct 29, 2025 at 05:19:54PM +0100, David Hildenbrand wrote:
> > > > > 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. :)

Ohhhh nice :)

I look forward to it!

>
> --
> Cheers
>
> David / dhildenb
>

Cheers, Lorenzo