Re: [PATCH v3] mm: introduce reference pages

[John Hubbard <jhubbard@nvidia.com>]

On 8/17/20 8:00 PM, Matthew Wilcox wrote:
> On Mon, Aug 17, 2020 at 07:31:39PM -0700, John Hubbard wrote:
>>>             Real time (s)    Max RSS (KiB)
>>> anon        2.237081         107088
>>> memset      2.252241         112180
>>> refpage     2.243786         107128
>>>
>>> We can see that RSS for refpage is almost the same as anon, and real
>>> time overhead is 44% that of memset.
>>>
>>
>> Are some of the numbers stale, maybe? Try as I might, I cannot combine
>> anything above to come up with 44%. :)
> 
> You're not trying hard enough ;-)
> 
> (2.252241 - 2.237081) / 2.237081 = .00677668801442594166
> (2.243786 - 2.237081) / 2.237081 = .00299720930981041812
> .00299720930981041812 / .00677668801442594166 = .44228232189973614648
> 
> tadaa!

haha, OK then! :) Next time I may try harder, but on the other hand my
interpretation of the results is still "this is a small effect", even
if there is a way to make it sound large by comparing the 3rd significant
digits of the results...

> 
> As I said last time this was posted, I'm just not excited by this.  We go
> from having a 0.68% time overhead down to an 0.30% overhead, which just
> doesn't move the needle for me.  Maybe there's a better benchmark than
> this to show benefits from this patchset.
> 

Yes, I wonder if there is an artificial workload that just uses refpages
really extensively, maybe we can get some good solid improvements shown
with that? Otherwise, it seems like we've just learned that memset is
actually pretty good in this case. :)

thanks,
-- 
John Hubbard
NVIDIA