Re: [PATCH v3 10/12] mm/gup: /proc/vmstat: pin_user_pages (FOLL_PIN) reporting

Kirill A. Shutemov
2020-02-03T21:30:14Z

On Mon, Feb 03, 2020 at 01:04:04PM -0800, John Hubbard wrote:
> On 2/3/20 5:53 AM, Kirill A. Shutemov wrote:
> > On Fri, Jan 31, 2020 at 07:40:27PM -0800, John Hubbard wrote:
> >> diff --git a/mm/gup.c b/mm/gup.c
> >> index c10d0d051c5b..9fe61d15fc0e 100644
> >> --- a/mm/gup.c
> >> +++ b/mm/gup.c
> >> @@ -29,6 +29,19 @@ struct follow_page_context {
> >> unsigned int page_mask;
> >> };
> >>
> >> +#ifdef CONFIG_DEBUG_VM
> >
> > Why under CONFIG_DEBUG_VM? There's nothing about this in the cover letter.
> >
>
> Early on, gup_benchmark showed a really significant slowdown from using these
> counters. And I don't doubt that it's still the case.
>
> I'll re-measure and add a short summary and a few numbers to the patch commit
> description, and to the v4 cover letter.

Looks like you'll show zeros for these counters if debug is off. It can be
confusing to the user. I think these counters should go away if you don't
count them.

--
Kirill A. Shutemov