Re: [PATCH 6/9] mm/swapfile: Make folio_dup_swap batchable

[Dev Jain]

On 10/03/26 1:57 pm, Kairui Song wrote:
> On Tue, Mar 10, 2026 at 3:36 PM Dev Jain <dev.jain@xxxxxxx> wrote:
>>
>> Teach folio_dup_swap to handle a batch of consecutive pages. Note that
>> folio_dup_swap already can handle a subset of this: nr_pages == 1 and
>> nr_pages == folio_nr_pages(folio). Generalize this to any nr_pages.
> 
> Thanks a lot for doing this. I was thinking it's about time we respin
> the batch unmapping of anon folios idea. Barry tried that before with
> an RFC, and now batching from swap side is easier, so some parts can
> be done cleaner.
> 
>> Currently we have a not-so-nice logic of passing in subpage == NULL if
>> we mean to exercise the logic on the entire folio, and subpage != NULL if
>> we want to exercise the logic on only that subpage. Remove this
>> indirection, and explicitly pass subpage != NULL, and the number of
>> pages required.
> 
> I was hoping most callers will just use the whole folio, but after
> checking your code, yeah, using explicit subpage and nr does fit the
> other parts better.
> 
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index 915bc93964dbd..eaf61ae6c3817 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -1738,7 +1738,8 @@ int folio_alloc_swap(struct folio *folio)
>>  /**
>>   * folio_dup_swap() - Increase swap count of swap entries of a folio.
>>   * @folio: folio with swap entries bounded.
>> - * @subpage: if not NULL, only increase the swap count of this subpage.
>> + * @subpage: Increase the swap count of this subpage till nr number of
>> + * pages forward.
> 
> The new nr_pages parameter isn't documented in the kernel-doc comment?

Oops, will add this in v2, thanks.