On Wed, Jun 08, 2022 at 10:14:32PM +0800, Miaohe Lin wrote:
> If folios were freed from under us, there's no need to reclaim them. Skip
> these folios to save lots of cpu cycles and avoid possible unnecessary
> disk I/O.
Yes, but I asked how often this happened, and you said you didn't know.
Do you have any data? I'm reluctant to make a function which is over
400 LOC already any longer.
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> ---
> v2:
> use folio_ref_freeze to guard against race with GUP (fast). Many thanks
> Matthew for pointing this out.
> ---
> mm/vmscan.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 13d34d9593bb..547ae7ae6ab1 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1610,13 +1610,19 @@ static unsigned int shrink_page_list(struct list_head *page_list,
> folio = lru_to_folio(page_list);
> list_del(&folio->lru);
>
> + nr_pages = folio_nr_pages(folio);
> +
> + if (folio_ref_count(folio) == 1 &&
> + folio_ref_freeze(folio, 1)) {
> + /* folio was freed from under us. So we are done. */
> + goto free_it;
> + }
> +
> if (!folio_trylock(folio))
> goto keep;
>
> VM_BUG_ON_FOLIO(folio_test_active(folio), folio);
>
> - nr_pages = folio_nr_pages(folio);
> -
> /* Account the number of base pages */
> sc->nr_scanned += nr_pages;
>
> --
> 2.23.0
>
