On 02/04/2024 14:10, Ryan Roberts wrote:
> On 28/03/2024 08:18, Barry Song wrote:
>> On Thu, Mar 28, 2024 at 3:45 AM Ryan Roberts <ryan.roberts@xxxxxxx> wrote:
>>>
>>> Now that swap supports storing all mTHP sizes, avoid splitting large
>>> folios before swap-out. This benefits performance of the swap-out path
>>> by eliding split_folio_to_list(), which is expensive, and also sets us
>>> up for swapping in large folios in a future series.
>>>
>>> If the folio is partially mapped, we continue to split it since we want
>>> to avoid the extra IO overhead and storage of writing out pages
>>> uneccessarily.
>>>
>>> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
>>> Reviewed-by: Barry Song <v-songbaohua@xxxxxxxx>
>>> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
>>> ---
>>> mm/vmscan.c | 9 +++++----
>>> 1 file changed, 5 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>> index 00adaf1cb2c3..293120fe54f3 100644
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -1223,11 +1223,12 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
>>> if (!can_split_folio(folio, NULL))
>>> goto activate_locked;
>>> /*
>>> - * Split folios without a PMD map right
>>> - * away. Chances are some or all of the
>>> - * tail pages can be freed without IO.
>>> + * Split partially mapped folios right
>>> + * away. We can free the unmapped pages
>>> + * without IO.
>>> */
>>> - if (!folio_entire_mapcount(folio) &&
>>> + if (data_race(!list_empty(
>>> + &folio->_deferred_list)) &&
>>> split_folio_to_list(folio,
>>> folio_list))
>>> goto activate_locked;
>>
>> Hi Ryan,
>>
>> Sorry for bringing up another minor issue at this late stage.
>
> No problem - I'd rather take a bit longer and get it right, rather than rush it
> and get it wrong!
>
>>
>> During the debugging of thp counter patch v2, I noticed the discrepancy between
>> THP_SWPOUT_FALLBACK and THP_SWPOUT.
>>
>> Should we make adjustments to the counter?
>
> Yes, agreed; we want to be consistent here with all the other existing THP
> counters; they only refer to PMD-sized THP. I'll make the change for the next
> version.
>
> I guess we will eventually want equivalent counters for per-size mTHP using the
> framework you are adding.
>
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 293120fe54f3..d7856603f689 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1241,8 +1241,10 @@ static unsigned int shrink_folio_list(struct
>> list_head *folio_list,
>> folio_list))
>> goto activate_locked;
>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> -
>> count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1);
>> - count_vm_event(THP_SWPOUT_FALLBACK);
>> + if (folio_test_pmd_mappable(folio)) {
This doesn't quite work because we have already split the folio here, so this
will always return false. I've changed it to:
if (nr_pages >= HPAGE_PMD_NR) {
>> +
>> count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1);
>> +
>> count_vm_event(THP_SWPOUT_FALLBACK);
>> + }
>> #endif
>> if (!add_to_swap(folio))
>> goto activate_locked_split;
>>
>>
>> Because THP_SWPOUT is only for pmd:
>>
>> static inline void count_swpout_vm_event(struct folio *folio)
>> {
>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> if (unlikely(folio_test_pmd_mappable(folio))) {
>> count_memcg_folio_events(folio, THP_SWPOUT, 1);
>> count_vm_event(THP_SWPOUT);
>> }
>> #endif
>> count_vm_events(PSWPOUT, folio_nr_pages(folio));
>> }
>>
>> I can provide per-order counters for this in my THP counter patch.
>>
>>> --
>>> 2.25.1
>>>
>>
>> Thanks
>> Barry
>
