Re: [gup] 17839856fd: stress-ng.vm-splice.ops_per_sec 2158.6% improvement

[Linus Torvalds]

On Mon, Jun 15, 2020 at 12:33 AM Jann Horn <jannh@xxxxxxxxxx> wrote:
>
> So in summary I guess the test was just really slow up until now
> because it was hitting a slowpath that you wouldn't hit during normal
> usage? At least for vmsplice(), writing uninitialized pages doesn't
> really make a whole lot of sense...

Heh. My main worry with that commit was that we'd see the reverse
effect: somebody implicitly depending on the continued sharing of
pages in some odd splice situation, and where breaking the COW would
result in a performance degradation.

The fact that it went the other way instead is somewhat ironic.

But good.

I guess I'll just ping the stable people to say "yeah, put that in
stable too". It's a fix, and apparently it _helps_ performance for the
degenerate cases rather than hurting anything.

             Linus