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

["Zi Yan" <ziy@nvidia.com>]

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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.

Let me know your thoughts.

-- 
Best Regards,
Yan, Zi


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