Re: [linux-next PATCH 1/2] mm: khugepaged: add exceed_max_ptes_* helpers

[Yang Shi]

On 4/30/20 2:59 PM, Kirill A. Shutemov wrote:
> On Thu, Apr 30, 2020 at 06:56:21AM +0800, Yang Shi wrote:
> > The max_ptes_{swap|none|shared} are defined to tune the behavior of
> > khugepaged.  The are checked at a couple of places with open coding.
> > Replace the opencoding to exceed_pax_ptes_{swap|none_shared} helpers to
> > improve the readability.
> >
> > Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> > Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> > Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> > ---
> >   mm/khugepaged.c | 27 +++++++++++++++++++++------
> >   1 file changed, 21 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index a02a4c5..0c8d30b 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -339,6 +339,21 @@ struct attribute_group khugepaged_attr_group = {
> >   };
> >   #endif /* CONFIG_SYSFS */
> >   
> > +static inline bool exceed_max_ptes_none(unsigned int *nr_ptes)
> > +{
> > +	return (++(*nr_ptes) > khugepaged_max_ptes_none);
> > +}
> > +
> > +static inline bool exceed_max_ptes_swap(unsigned int *nr_ptes)
> > +{
> > +	return (++(*nr_ptes) > khugepaged_max_ptes_swap);
> > +}
> > +
> > +static inline bool exceed_max_ptes_shared(unsigned int *nr_ptes)
> > +{
> > +	return (++(*nr_ptes) > khugepaged_max_ptes_shared);
> > +}
> > +
> Frankly, I find this ugly and confusing. Open-coded version is more
> readable to me.

I'm sorry you feel that way. I tend to agree that dereference looks not 
good. The open-coded version is not hard to understand to me either.

They are checked at a couple of different places with different 
variables, i.e. unmapped vs swap, and with different comparisons, > vs 
<=. I just thought the helpers with unified name started with "exceed_" 
may make it more self-explained and readable. Anyway this totally 
depends on taste and I really don't insist on this change.

>