Re: [PATCH v2 3/3] memory tiering: count PGPROMOTE_SUCCESS when mem tiering is enabled.

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2024/7/23 21:03, Zi Yan wrote:
> On Tue Jul 23, 2024 at 6:17 AM EDT, David Hildenbrand wrote:
>> On 23.07.24 05:24, Kefeng Wang wrote:
>>>
>>>
>>> On 2024/7/23 9:54, Zi Yan wrote:
>>>> On Mon Jul 22, 2024 at 9:48 PM EDT, Kefeng Wang wrote:
>>>>>
>>>>>
>>>>> On 2024/7/23 1:29, Zi Yan wrote:
>>>>>> memory tiering can be enabled/disabled at runtime and
>>>>>> sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING is used to check
>>>>>> it. In migrate_misplaced_folio(), the check is missing when
>>>>>> PGPROMOTE_SUCCESS is incremented. Add the missing check.
>>>>>>
>>>>>> Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>>>>>> Closes: https://lore.kernel.org/linux-mm/f4ae2c9c-fe40-4807-bdb2-64cf2d716c1a@huawei.com/
>>>>>> Fixes: 33024536bafd ("memory tiering: hot page selection with hint page fault latency")
>>>>>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>>>>>
>>>>> Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>>>>>
>>>> Thanks.
>>>>
>>>>>> ---
>>>>>>      mm/migrate.c | 4 +++-
>>>>>>      1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/mm/migrate.c b/mm/migrate.c
>>>>>> index bdbb5bb04c91..b819809da470 100644
>>>>>> --- a/mm/migrate.c
>>>>>> +++ b/mm/migrate.c
>>>>>> @@ -2630,7 +2630,9 @@ int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
>>>>>>      		putback_movable_pages(&migratepages);
>>>>>>      	if (nr_succeeded) {
>>>>>>      		count_vm_numa_events(NUMA_PAGE_MIGRATE, nr_succeeded);
>>>>>> -		if (!node_is_toptier(folio_nid(folio)) && node_is_toptier(node))
>>>>>> +		if ((sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING)
>>>>>> +		    && !node_is_toptier(folio_nid(folio))
>>>>>> +		    && node_is_toptier(node))
>>>>>>      			mod_node_page_state(pgdat, PGPROMOTE_SUCCESS,
>>>>>>      					    nr_succeeded);
>>>>>
>>>>> The should be in advance of patch2, and change above to use
>>>>> folio_has_cpupid() helper() too.
>>>>
>>>> It shares the same logic of !folio_has_cpupid() but it might be confusing to
>>>> put !folio_has_cpupid(folio) && node_is_toptier(node) here. folio's
>>>> cpupid has nothing to do with the stats here, thus I did not use the
>>>> function.
>>>
>>> If folio don't include access time, we do migrate it but it isn't a
>>> promotion, so don't count it, other comments?
>>>
>>> PS: Could we rename folio_has_cpupid() to folio_has_access_time(), even
>>> without memory_tiering, we still have cpupid in folio, right?
> 
> folio_has_access_time() would be the opposite of folio_has_cpupid().
> If memory tiering is off (either at compile time or dynamically), a
> folio has cpupid all the time.
> 
>>
>> Maybe call it "folio_use_cpupid()" or sth like that? The "has" is a bit
>> misleading, because the folio has a cpuid in any case, no?
> 
> The folio's cpupid field is reused to record page access time, when the folio
> is !node_is_toptier() and memory tiering mode is on.
> 
> In sum, using folio_use_access_time() as !folio_has_cpupid() seems
> better to me, since it covers the special use of folio's cpupid field.
> 

It sounds good, thanks.

> Let me know your thoughts.
>