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

Yang Shi
2020-04-30T23:59:41Z

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@linux.intel.com>
>> Cc: Hugh Dickins <hughd@google.com>
>> Cc: Andrea Arcangeli <aarcange@redhat.com>
>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
>> ---
>> 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.

>