Re: [PATCH v2 1/9] mm: vmscan: add validation before spliting shmem large folio

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 2024/6/20 14:12, Yu Zhao wrote:
> On Tue, Jun 18, 2024 at 12:54 AM Baolin Wang
> <baolin.wang@linux.alibaba.com> wrote:
>>
>> Add swap available space validation before spliting shmem large folio to
>> avoid redundant split, since we can not write shmem folio to the swap device
>> in this case.
> 
> We don't scan anon LRU unless we know we may be able to swap. Even if
> there is swap space, we may still not be able to swap. See
> can_reclaim_anon_pages().

Right. Another case is MADV_PAGEOUT can still split a large shmem folio 
even without a swap device. I know this is not a common case, and I can 
drop this patch if it is less helpful.

Thanks for your input.

>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>> ---
>>   mm/vmscan.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 1807e5d95dda..61465f92283f 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1237,6 +1237,14 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
>>                          }
>>                  } else if (folio_test_swapbacked(folio) &&
>>                             folio_test_large(folio)) {
>> +
>> +                       /*
>> +                        * Do not split shmem folio if no swap memory
>> +                        * available.
>> +                        */
>> +                       if (!total_swap_pages)
>> +                               goto activate_locked;
>> +
>>                          /* Split shmem folio */
>>                          if (split_folio_to_list(folio, folio_list))
>>                                  goto keep_locked;
>> --
>> 2.39.3
>>
>>