On 15/03/2024 10:43, David Hildenbrand wrote:
> On 11.03.24 16:00, Ryan Roberts 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.
>>
>> 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 cf7d4cf47f1a..0ebec99e04c6 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1222,11 +1222,12 @@ 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 map
>> + * right away. Chances are some or all
>> + * of the tail pages can be freed
>> + * without IO.
>> */
>> - if (!folio_entire_mapcount(folio) &&
>> + if (!list_empty(&folio->_deferred_list) &&
>> split_folio_to_list(folio,
>> folio_list))
>> goto activate_locked;
>
> Not sure if we might have to annotate that with data_race().
I asked that exact question to Matthew in another context bt didn't get a
response. There are examples of checking if the deferred list is empty with and
without data_race() in the code base. But list_empty() is implemented like this:
static inline int list_empty(const struct list_head *head)
{
return READ_ONCE(head->next) == head;
}
So I assumed the READ_ONCE() makes everything safe without a lock? Perhaps not
sufficient for KCSAN?
>
> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
>
Thanks!
