On Sun, Jan 16, 2022 at 12:18:14PM +0000, Matthew Wilcox (Oracle) wrote:
> We have to allocate memory in order to split a file-backed folio, so
> it's not a good idea to split them in the memory freeing path.
Could elaborate on why split a file-backed folio requires memory
allocation?
> It also
> doesn't work for XFS because pages have an extra reference count from
> page_has_private() and split_huge_page() expects that reference to have
> already been removed.
Need to adjust can_split_huge_page()?
> Unfortunately, we still have to split shmem THPs
> because we can't handle swapping out an entire THP yet.
... especially if the system doesn't have swap :P
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> mm/vmscan.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 700434db5735..45665874082d 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1728,8 +1728,8 @@ static unsigned int shrink_page_list(struct list_head *page_list,
> /* Adding to swap updated mapping */
> mapping = page_mapping(page);
> }
> - } else if (unlikely(PageTransHuge(page))) {
> - /* Split file THP */
> + } else if (PageSwapBacked(page) && PageTransHuge(page)) {
> + /* Split shmem THP */
> if (split_huge_page_to_list(page, page_list))
> goto keep_locked;
> }
> --
> 2.34.1
>
--
Kirill A. Shutemov
