On Thu, Jan 10, 2019 at 8:58 PM Dominique Martinet
[off-list ref] wrote:

I get on average over a few queries approximately a real time of 350ms,
230ms and 220ms immediately after drop cache and service restart, and
150ms, 60ms and 60ms after a prefetch (hand-wavy average over 3 runs, I
didn't have the patience to do proper testing).
(In both cases, user/sys are less than 10ms; I don't see much difference
there)

But those numbers aren't about the mincore() change. That's just from
dropping caches.

Now, what's the difference with the mincore change, and without? Is it
actually measurable?

Because that's all that matters: is the mincore change something you
can even notice? Is it a big regression?

The fact that things are slower when they are cold in the cache isn't
the issue. The issue is whether the change to mincore semantics makes
any difference to real loads.

                Linus