On Thu, Aug 20, 2020 at 2:54 PM Peter Xu <peterx@redhat.com> wrote:
>
> I kind of prefer the new suggestion to remove code rather than adding new
> codes.  I definitely don't know enough on the side effect of it, especially
> performance-wise on either ksm or swap, but... IIUC the worst case is we'll get
> some perf report later on, and it seems also not hard to revert the patch later
> if we want.

Well, would you be willing to try this patch out?

After you apply that patch, you should be able to remove the
should_force_cow_break() games entirely, because a write to the page
should always break cow towards the writer if there are any GUP users
around (put another way: away from the GUP).

However, to make the test meaningful, it really should do some swap testing too.

            Linus