Re: [RFC PATCH v2 9/9] docs: mm: update THP swapin counter descriptions

[Fujunjie <fujunjie1@qq.com>]

On 5/30/2026 2:37 AM, Nhat Pham wrote:
> On Fri, May 29, 2026 at 5:19 AM fujunjie <fujunjie1@qq.com> wrote:
>>
>> The THP swapin counter descriptions still describe large swapin as
>> coming only from non-zswap swap devices. Update them now that
>> zswap-backed large folio swapin can also increment swpin.
>>
>> Also describe policy and backend rejection as swpin_fallback cases,
>> since speculative zswap large swapin can intentionally fall back before
>> doing large IO.
>>
>> Signed-off-by: fujunjie <fujunjie1@qq.com>
>> ---
>>  Documentation/admin-guide/mm/transhuge.rst | 11 ++++++-----
>>  1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
>> index 23f8d13c2629..59b7a0d09243 100644
>> --- a/Documentation/admin-guide/mm/transhuge.rst
>> +++ b/Documentation/admin-guide/mm/transhuge.rst
>> @@ -667,13 +667,14 @@ zswpout
>>         piece without splitting.
>>
>>  swpin
>> -       is incremented every time a huge page is swapped in from a non-zswap
>> -       swap device in one piece.
>> +       is incremented every time a huge page is swapped in from swap or
>> +       zswap in one piece.
>>
>>  swpin_fallback
>> -       is incremented if swapin fails to allocate or charge a huge page
>> -       and instead falls back to using huge pages with lower orders or
>> -       small pages.
>> +       is incremented if swapin cannot use a huge page and instead falls
>> +       back to using huge pages with lower orders or small pages. This can
>> +       happen because allocation or charging fails, or because policy or
>> +       backend state rejects a speculative large swapin.
> 
> I think we should add separate zswpin and zswpin fallback counter for
> THP rather than overloading swpin. We already do that for zswpout vs
> swpout.

that makes sense.