On Fri 13-09-19 12:18:49, Kirill A. Shutemov wrote:
> Adding fully unmapped pages into deferred split queue is not productive:
> these pages are about to be freed or they are pinned and cannot be split
> anyway.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> mm/rmap.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 003377e24232..45388f1bf317 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1271,12 +1271,20 @@ static void page_remove_anon_compound_rmap(struct page *page)
> if (TestClearPageDoubleMap(page)) {
> /*
> * Subpages can be mapped with PTEs too. Check how many of
> - * themi are still mapped.
> + * them are still mapped.
> */
> for (i = 0, nr = 0; i < HPAGE_PMD_NR; i++) {
> if (atomic_add_negative(-1, &page[i]._mapcount))
> nr++;
> }
> +
> + /*
> + * Queue the page for deferred split if at least one small
> + * page of the compound page is unmapped, but at least one
> + * small page is still mapped.
> + */
> + if (nr && nr < HPAGE_PMD_NR)
> + deferred_split_huge_page(page);
You've set nr to zero in the for loop so this cannot work AFAICS.
> } else {
> nr = HPAGE_PMD_NR;
> }
> @@ -1284,10 +1292,8 @@ static void page_remove_anon_compound_rmap(struct page *page)
> if (unlikely(PageMlocked(page)))
> clear_page_mlock(page);
>
> - if (nr) {
> + if (nr)
> __mod_node_page_state(page_pgdat(page), NR_ANON_MAPPED, -nr);
> - deferred_split_huge_page(page);
> - }
> }
>
> /**
> --
> 2.21.0
--
Michal Hocko
SUSE Labs
