Re: [PATCH v9 1/8] mm: Add per-cpu logic to page shuffling

From: Alexander Duyck
Date: Tue Sep 10 2019 - 18:11:59 EST

On Mon, 2019-09-09 at 10:14 +0200, David Hildenbrand wrote:
> On 07.09.19 19:25, Alexander Duyck wrote:
> > From: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> >
> > Change the logic used to generate randomness in the suffle path so that we
> > can avoid cache line bouncing. The previous logic was sharing the offset
> > and entropy word between all CPUs. As such this can result in cache line
> > bouncing and will ultimately hurt performance when enabled.
> So, usually we perform such changes if there is real evidence. Do you
> have any such performance numbers to back your claims?

I don't have any numbers. From what I can tell the impact is small enough
that this doesn't really have much impact.

With that being the case I can probably just drop this patch. I will
instead just use "rand & 1" in the 2nd patch to generate the return value
which was what was previously done in add_to_free_area_random.