Re: PROBLEM: userfaultfd REGISTER minor mode on MAP_PRIVATE range fails

[Peter Xu <peterx@redhat.com>]

On Tue, Sep 16, 2025 at 11:52:18AM -0400, David P. Reed wrote:
> synchronous would be better. But what I want to do is at least get
> notifications of swapin events (including the case when the page is in
> swap cache). Also, using UFFDIO_COPY can be useful for the swap in case
> might make sense (but rarely, because there's no way to access the data
> that was swapped out).

Some more info on the use case might be helpful.  I can start with some
more questions if that helps.

- If it's about page hotness / coldness, have you tried existing facilities
  (page idle, DAMON, etc.)?  If so, why they won't work?

- Assuming it's async reports that can be collected, what do you plan to do
  with the info?  Do you care about swap outs prior to swap ins?

- How sync events would be better in this case?

Thanks,

-- 
Peter Xu