Re: Why sometimes count vm event with page number, sometimes not?

[Vlastimil Babka <vbabka@suse.cz>]

On 11/5/19 7:28 AM, Wei Yang wrote:
> On Mon, Nov 04, 2019 at 07:32:51PM -0800, Matthew Wilcox wrote:
>> On Tue, Nov 05, 2019 at 10:26:44AM +0800, Wei Yang wrote:
>>> Hi, All,
>>>
>>> I am curious about the semantic of __count_vm_event[s].
>>>
>>> For example, we count PGDEACTIVATE event in lru_deactivate_file_fn() and
>>> lru_deactivate_fn(). One of them count with number of page, the other not.
>>>
>>> Just curious about the exact value we want to count.
>>
>> I don't understand the question.  We deactivate one page
>> in lru_deactivate_file_fn().  We deactivate several pages in
>> shrink_active_list().  PGDEACTIVATE counts the number of pages which
>> have been deactivated.
>>
>> Does that answer your question?
> 
> Not yet.
> 
> In function, lru_deactivate_fn(), __count_vm_events's second parameter is
> hpage_nr_pages(page). This is the number in size of "normal" page. Per my
> understanding, the page deactivated in lru_deactivate_file_fn() could be a
> hpage too. But it just count the deactivation once instead of
> hpage_nr_pages().
> 
> Or you want to say the page deactivated in lru_deactivate_file_fn() must be an
> order 0 page?

I suspect that was true before THP on shmem, but now perhaps it's not
true anymore? CCing Kirill and Hugh.