On 2022/3/31 16:38, Huang, Ying wrote:
> Miaohe Lin <linmiaohe@xxxxxxxxxx> writes:
>
>> can_split_huge_page is introduced via commit b8f593cd0896 ("mm, THP, swap:
>> check whether THP can be split firstly") to avoid deleting the THP from
>> the swap cache and freeing the swap cluster when the THP cannot be split.
>> But since commit bd4c82c22c36 ("mm, THP, swap: delay splitting THP after
>> swapped out"), splitting THP is delayed until THP is swapped out. There's
>> no need to delete the THP from the swap cache and free the swap cluster
>> anymore. Thus we can remove this unneeded can_split_huge_page check now to
>> simplify the code logic.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>> ---
>> mm/vmscan.c | 3 ---
>> 1 file changed, 3 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 7c1a9713bfc9..09b452c4d256 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1691,9 +1691,6 @@ static unsigned int shrink_page_list(struct list_head *page_list,
>> 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
>
> I'm OK with the change itself. But THP still needs to be split after
> being swapped out. The reason we don't need to check can_split_folio()
Could you please explain the relevant code path more detailed slightly?
IIUC, if THP is swapped out, it will be freed via destroy_compound_page
after __remove_mapping in shrink_page_list. So THP can be freed without
split. Or am I miss something ?
> is that folio_maybe_dma_pinned() is checked before. Which 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 as follows,
>
> /*
> * 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) && !compound_mapcount(page) &&
> split_huge_page_to_list(page, page_list))
> goto keep_locked;
>
> activate_locked can be changed to keep_locked too, because it's just
> short term pinning.
>
The change above looks good to me. Many thanks. Should I add a Suggested-by
tag for you?
> Best Regards,
> Huang, Ying
Thanks.
>
> .
>
