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

[John Hubbard]

On 2/3/20 1:30 PM, Kirill A. Shutemov wrote:
> 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.
> 

OK, that's a good point. (And in fact, the counters==0 situation already led me
astray briefly while debugging with Leon R, even. heh.) I'll remove them entirely for
the !CONFIG_DEBUG_VM case.

thanks,
-- 
John Hubbard
NVIDIA