Re: [PATCH v10 3/6] mm: Introduce Reported pages

David Hildenbrand
2019-09-23T15:47:42Z

On 23.09.19 17:45, David Hildenbrand wrote:
> On 23.09.19 17:37, Michael S. Tsirkin wrote:
>> On Mon, Sep 23, 2019 at 08:28:00AM -0700, Alexander Duyck wrote:
>>> On Mon, Sep 23, 2019 at 8:00 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>>>>
>>>> On Mon, Sep 23, 2019 at 07:50:15AM -0700, Alexander Duyck wrote:
>>>>>>> +static inline void
>>>>>>> +page_reporting_reset_boundary(struct zone *zone, unsigned int order, int mt)
>>>>>>> +{
>>>>>>> + int index;
>>>>>>> +
>>>>>>> + if (order < PAGE_REPORTING_MIN_ORDER)
>>>>>>> + return;
>>>>>>> + if (!test_bit(ZONE_PAGE_REPORTING_ACTIVE, &zone->flags))
>>>>>>> + return;
>>>>>>> +
>>>>>>> + index = get_reporting_index(order, mt);
>>>>>>> + reported_boundary[index] = &zone->free_area[order].free_list[mt];
>>>>>>> +}
>>>>>>
>>>>>> So this seems to be costly.
>>>>>> I'm guessing it's the access to flags:
>>>>>>
>>>>>>
>>>>>> /* zone flags, see below */
>>>>>> unsigned long flags;
>>>>>>
>>>>>> /* Primarily protects free_area */
>>>>>> spinlock_t lock;
>>>>>>
>>>>>>
>>>>>>
>>>>>> which is in the same cache line as the lock.
>>>>>
>>>>> I'm not sure what you mean by this being costly?
>>>>
>>>> I've just been wondering why does will it scale report a 1.5% regression
>>>> with this patch.
>>>
>>> Are you talking about data you have collected from a test you have
>>> run, or the data I have run?
>>
>> About the kernel test robot auto report that was sent recently.
>
> https://lkml.org/lkml/2019/9/21/112
>
> And if I'm correct, that regression is observable in case reporting is
> not enabled. (so with this patch applied only, e.g., on a bare-metal system)
>

To be even more precise: # CONFIG_PAGE_REPORTING is not set

--

Thanks,

David / dhildenb