Re: [PATCH v2 0/3] skip redundant TLB sync IPIs

[Dave Hansen]

On 12/29/25 06:52, Lance Yang wrote:
...
> This series introduces a way for architectures to indicate their TLB flush
> already provides full synchronization, allowing the redundant IPI to be
> skipped. For now, the optimization is implemented for x86 first and applied
> to all page table operations that free or unshare tables.

I really don't like all the complexity here. Even on x86, there are
three or more ways of deriving this. Having the pv_ops check the value
of another pv op is also a bit unsettling.

That said, complexity can be worth it with sufficient demonstrated
gains. But:

> When unsharing hugetlb PMD page tables or collapsing pages in khugepaged,
> we send two IPIs: one for TLB invalidation, and another to synchronize
> with concurrent GUP-fast walkers.

Those aren't exactly hot paths. khugepaged is fundamentally rate
limited. I don't think unsharing hugetlb PMD page tables just is all
that common either.

What kind of end user benefit is there to justify the complexity?