On Fri, Jan 18, 2019 at 9:45 AM Vlastimil Babka [off-list ref] wrote:

Or maybe we could resort to the 5.0-rc1 page table check (that is now being
reverted) but only in cases when we are not allowed the page cache residency
check? Or would that be needlessly complicated?

I think it would  be good fallback semantics, but I'm not sure it's
worth it. Have you tried writing a patch for it? I don't think you'd
want to do the check *when* you find a hole, so you'd have to do it
upfront and then pass the cached data down with the private pointer
(or have a separate "struct mm_walk" structure, perhaps?

So I suspect we're better off with the patch we have. But if somebody
*wants* to try to do that fancier patch, and it doesn't look
horrendous, I think it might be the "quality" solution.

              Linus