On 2022/4/12 16:59, Oscar Salvador wrote:
> On Sat, Apr 09, 2022 at 05:34:53PM +0800, Miaohe Lin wrote:
>> We don't need to check can_split_folio() because folio_maybe_dma_pinned()
>> is checked before. It will avoid the long term pinned pages to be swapped
>> out. And we can live with short term pinned pages. Without can_split_folio
>> checking we can simplify the code. Also activate_locked can be changed to
>> keep_locked as it's just short term pinning.
>
> What do you mean by "we can live with short term pinned pages"?
> Does it mean that it was not pinned when we check
> folio_maybe_dma_pinned() but now it is?
>
> To me it looks like the pinning is fluctuating and we rely on
> split_folio_to_list() to see whether we succeed or not, and if not
> we give it another spin in the next round?
Yes. Short term pinned pages is relative to long term pinned pages and these pages won't be
pinned for a noticeable time. So it's expected to split the folio successfully in the next
round as the pinning is really fluctuating. Or am I miss something?
Many thanks for your comment and reply!
>
>> Suggested-by: Huang, Ying <ying.huang@xxxxxxxxx>
>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>> ---
>> mm/vmscan.c | 22 ++++++++--------------
>> 1 file changed, 8 insertions(+), 14 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 4a76be47bed1..01f5db75a507 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1711,20 +1711,14 @@ static unsigned int shrink_page_list(struct list_head *page_list,
>> goto keep_locked;
>> if (folio_maybe_dma_pinned(folio))
>> goto keep_locked;
>> - if (PageTransHuge(page)) {
>> - /* cannot split THP, skip it */
>> - if (!can_split_folio(folio, NULL))
>> - goto activate_locked;
>> - /*
>> - * Split pages without a PMD map right
>> - * away. Chances are some or all of the
>> - * tail pages can be freed without IO.
>> - */
>> - if (!folio_entire_mapcount(folio) &&
>> - split_folio_to_list(folio,
>> - page_list))
>> - goto activate_locked;
>> - }
>> + /*
>> + * Split pages without a PMD map right
>> + * away. Chances are some or all of the
>> + * tail pages can be freed without IO.
>> + */
>> + if (PageTransHuge(page) && !folio_entire_mapcount(folio) &&
>> + split_folio_to_list(folio, page_list))
>> + goto keep_locked;
>> if (!add_to_swap(page)) {
>> if (!PageTransHuge(page))
>> goto activate_locked_split;
>> --
>> 2.23.0
>>
>>
>
