On Fri 15-11-19 02:24:29, Yang Shi wrote:
> When doing migration if the freed page is met, we just return without
> migrating it since it is pointless to migrate a freed page. But, the
> current code allocates target page unconditionally before handling freed
> page, if the page is freed, the newly allocated will be just freed. It
> doesn't make too much sense and is just a waste of time although
> migrating freed page is rare.
>
> So, handle freed page at the before that to avoid unnecessary page
> allocation and free.
>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
I would be really surprised if this led to any runtime visible effect
but I do agree that one less put_page path looks slightly better. For
that reason
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> v2: * Keep thp migration support check before handling freed page per Michal Hocko
> * Fixed the build warning reported by 0-day
>
> mm/migrate.c | 14 +++++---------
> 1 file changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 4fe45d1..a8f87cb 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1168,15 +1168,11 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
> enum migrate_reason reason)
> {
> int rc = MIGRATEPAGE_SUCCESS;
> - struct page *newpage;
> + struct page *newpage = NULL;
>
> if (!thp_migration_supported() && PageTransHuge(page))
> return -ENOMEM;
>
> - newpage = get_new_page(page, private);
> - if (!newpage)
> - return -ENOMEM;
> -
> if (page_count(page) == 1) {
> /* page was freed from under us. So we are done. */
> ClearPageActive(page);
> @@ -1187,13 +1183,13 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
> __ClearPageIsolated(page);
> unlock_page(page);
> }
> - if (put_new_page)
> - put_new_page(newpage, private);
> - else
> - put_page(newpage);
> goto out;
> }
>
> + newpage = get_new_page(page, private);
> + if (!newpage)
> + return -ENOMEM;
> +
> rc = __unmap_and_move(page, newpage, force, mode);
> if (rc == MIGRATEPAGE_SUCCESS)
> set_page_owner_migrate_reason(newpage, reason);
> --
> 1.8.3.1
>
--
Michal Hocko
SUSE Labs
