Re: [PATCH 2/2] mm: fix numa stats for thp migration

[Shakeel Butt <shakeelb@google.com>]

On Sun, Dec 27, 2020 at 10:14 AM Shakeel Butt <shakeelb@google.com> wrote:
>
> Currently the kernel is not correctly updating the numa stats for
> NR_FILE_PAGES and NR_SHMEM on THP migration. Fix that. For NR_FILE_DIRTY
> and NR_ZONE_WRITE_PENDING, although at the moment there is no need to
> handle THP migration as kernel still does not have write support for
> file THP but to be more future proof, this patch adds the THP support
> for those stats as well.
>
> Fixes: e71769ae52609 ("mm: enable thp migration for shmem thp")
> Signed-off-by: Shakeel Butt <shakeelb@google.com>
> Cc: <stable@vger.kernel.org>
> ---
>  mm/migrate.c | 23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 613794f6a433..ade163c6ecdf 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -402,6 +402,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
>         struct zone *oldzone, *newzone;
>         int dirty;
>         int expected_count = expected_page_refs(mapping, page) + extra_count;
> +       int nr = thp_nr_pages(page);
>
>         if (!mapping) {
>                 /* Anonymous page without mapping */
> @@ -437,7 +438,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
>          */
>         newpage->index = page->index;
>         newpage->mapping = page->mapping;
> -       page_ref_add(newpage, thp_nr_pages(page)); /* add cache reference */
> +       page_ref_add(newpage, nr); /* add cache reference */
>         if (PageSwapBacked(page)) {
>                 __SetPageSwapBacked(newpage);
>                 if (PageSwapCache(page)) {
> @@ -459,7 +460,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
>         if (PageTransHuge(page)) {
>                 int i;
>
> -               for (i = 1; i < HPAGE_PMD_NR; i++) {
> +               for (i = 1; i < nr; i++) {
>                         xas_next(&xas);
>                         xas_store(&xas, newpage);
>                 }
> @@ -470,7 +471,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
>          * to one less reference.
>          * We know this isn't the last reference.
>          */
> -       page_ref_unfreeze(page, expected_count - thp_nr_pages(page));
> +       page_ref_unfreeze(page, expected_count - nr);
>
>         xas_unlock(&xas);
>         /* Leave irq disabled to prevent preemption while updating stats */
> @@ -493,17 +494,17 @@ int migrate_page_move_mapping(struct address_space *mapping,
>                 old_lruvec = mem_cgroup_lruvec(memcg, oldzone->zone_pgdat);
>                 new_lruvec = mem_cgroup_lruvec(memcg, newzone->zone_pgdat);
>
> -               __dec_lruvec_state(old_lruvec, NR_FILE_PAGES);
> -               __inc_lruvec_state(new_lruvec, NR_FILE_PAGES);
> +               __mod_lruvec_state(old_lruvec, NR_FILE_PAGES, -nr);
> +               __mod_lruvec_state(new_lruvec, NR_FILE_PAGES, nr);
>                 if (PageSwapBacked(page) && !PageSwapCache(page)) {
> -                       __dec_lruvec_state(old_lruvec, NR_SHMEM);
> -                       __inc_lruvec_state(new_lruvec, NR_SHMEM);
> +                       __mod_lruvec_state(old_lruvec, NR_SHMEM, -nr);
> +                       __mod_lruvec_state(new_lruvec, NR_SHMEM, nr);
>                 }
>                 if (dirty && mapping_can_writeback(mapping)) {
> -                       __dec_lruvec_state(old_lruvec, NR_FILE_DIRTY);
> -                       __dec_zone_state(oldzone, NR_ZONE_WRITE_PENDING);
> -                       __inc_lruvec_state(new_lruvec, NR_FILE_DIRTY);
> -                       __inc_zone_state(newzone, NR_ZONE_WRITE_PENDING);
> +                       __mod_lruvec_state(old_lruvec, NR_FILE_DIRTY, -nr);
> +                       __mod_zone_page_tate(oldzone, NR_ZONE_WRITE_PENDING, -nr);

This should be __mod_zone_page_state(). I fixed locally but sent the
older patch by mistake.

> +                       __mod_lruvec_state(new_lruvec, NR_FILE_DIRTY, nr);
> +                       __mod_zone_page_state(newzone, NR_ZONE_WRITE_PENDING, nr);
>                 }
>         }
>         local_irq_enable();
> --
> 2.29.2.729.g45daf8777d-goog
>