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)) {
> +
> 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
