Re: [PATCH v1 3/5] mm/page_alloc: always move pages to the tail of the freelist in unset_migratetype_isolate()

Michal Hocko
2020-10-02T13:24:08Z

On Mon 28-09-20 20:21:08, David Hildenbrand wrote:
> Page isolation doesn't actually touch the pages, it simply isolates
> pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>
> We already place pages to the tail of the freelists when undoing
> isolation via __putback_isolated_page(), let's do it in any case
> (e.g., if order <= pageblock_order) and document the behavior.
>
> Add a "to_tail" parameter to move_freepages_block() but introduce a
> a new move_to_free_list_tail() - similar to add_to_free_list_tail().
>
> This change results in all pages getting onlined via online_pages() to
> be placed to the tail of the freelist.

Is there anything preventing to do this unconditionally? Or in other
words is any of the existing callers of move_freepages_block benefiting
from adding to the head?

> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Scott Cheloha <cheloha@linux.ibm.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> include/linux/page-isolation.h | 4 ++--
> mm/page_alloc.c | 35 +++++++++++++++++++++++-----------
> mm/page_isolation.c | 12 +++++++++---
> 3 files changed, 35 insertions(+), 16 deletions(-)
>
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index 572458016331..3eca9b3c5305 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -36,8 +36,8 @@ static inline bool is_migrate_isolate(int migratetype)
> struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> int migratetype, int flags);
> void set_pageblock_migratetype(struct page *page, int migratetype);
> -int move_freepages_block(struct zone *zone, struct page *page,
> - int migratetype, int *num_movable);
> +int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
> + bool to_tail, int *num_movable);
>
> /*
> * Changes migrate type in [start_pfn, end_pfn) to be MIGRATE_ISOLATE.
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9e3ed4a6f69a..d5a5f528b8ca 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -905,6 +905,15 @@ static inline void move_to_free_list(struct page *page, struct zone *zone,
> list_move(&page->lru, &area->free_list[migratetype]);
> }
>
> +/* Used for pages which are on another list */
> +static inline void move_to_free_list_tail(struct page *page, struct zone *zone,
> + unsigned int order, int migratetype)
> +{
> + struct free_area *area = &zone->free_area[order];
> +
> + list_move_tail(&page->lru, &area->free_list[migratetype]);
> +}
> +
> static inline void del_page_from_free_list(struct page *page, struct zone *zone,
> unsigned int order)
> {
> @@ -2338,9 +2347,9 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
> * Note that start_page and end_pages are not aligned on a pageblock
> * boundary. If alignment is required, use move_freepages_block()
> */
> -static int move_freepages(struct zone *zone,
> - struct page *start_page, struct page *end_page,
> - int migratetype, int *num_movable)
> +static int move_freepages(struct zone *zone, struct page *start_page,
> + struct page *end_page, int migratetype,
> + bool to_tail, int *num_movable)
> {
> struct page *page;
> unsigned int order;
> @@ -2371,7 +2380,10 @@ static int move_freepages(struct zone *zone,
> VM_BUG_ON_PAGE(page_zone(page) != zone, page);
>
> order = page_order(page);
> - move_to_free_list(page, zone, order, migratetype);
> + if (to_tail)
> + move_to_free_list_tail(page, zone, order, migratetype);
> + else
> + move_to_free_list(page, zone, order, migratetype);
> page += 1 << order;
> pages_moved += 1 << order;
> }
> @@ -2379,8 +2391,8 @@ static int move_freepages(struct zone *zone,
> return pages_moved;
> }
>
> -int move_freepages_block(struct zone *zone, struct page *page,
> - int migratetype, int *num_movable)
> +int move_freepages_block(struct zone *zone, struct page *page, int migratetype,
> + bool to_tail, int *num_movable)
> {
> unsigned long start_pfn, end_pfn;
> struct page *start_page, *end_page;
> @@ -2401,7 +2413,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
> return 0;
>
> return move_freepages(zone, start_page, end_page, migratetype,
> - num_movable);
> + to_tail, num_movable);
> }
>
> static void change_pageblock_range(struct page *pageblock_page,
> @@ -2526,8 +2538,8 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
> if (!whole_block)
> goto single_page;
>
> - free_pages = move_freepages_block(zone, page, start_type,
> - &movable_pages);
> + free_pages = move_freepages_block(zone, page, start_type, false,
> + &movable_pages);
> /*
> * Determine how many pages are compatible with our allocation.
> * For movable allocation, it's the number of movable pages which
> @@ -2635,7 +2647,8 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
> && !is_migrate_cma(mt)) {
> zone->nr_reserved_highatomic += pageblock_nr_pages;
> set_pageblock_migratetype(page, MIGRATE_HIGHATOMIC);
> - move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, NULL);
> + move_freepages_block(zone, page, MIGRATE_HIGHATOMIC, false,
> + NULL);
> }
>
> out_unlock:
> @@ -2711,7 +2724,7 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
> */
> set_pageblock_migratetype(page, ac->migratetype);
> ret = move_freepages_block(zone, page, ac->migratetype,
> - NULL);
> + false, NULL);
> if (ret) {
> spin_unlock_irqrestore(&zone->lock, flags);
> return ret;
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index abfe26ad59fd..de44e1329706 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -45,7 +45,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
> set_pageblock_migratetype(page, MIGRATE_ISOLATE);
> zone->nr_isolate_pageblock++;
> nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
> - NULL);
> + false, NULL);
>
> __mod_zone_freepage_state(zone, -nr_pages, mt);
> spin_unlock_irqrestore(&zone->lock, flags);
> @@ -83,7 +83,7 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> * Because freepage with more than pageblock_order on isolated
> * pageblock is restricted to merge due to freepage counting problem,
> * it is possible that there is free buddy page.
> - * move_freepages_block() doesn't care of merge so we need other
> + * move_freepages_block() don't care about merging, so we need another
> * approach in order to merge them. Isolation and free will make
> * these pages to be merged.
> */
> @@ -106,9 +106,15 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> * If we isolate freepage with more than pageblock_order, there
> * should be no freepage in the range, so we could avoid costly
> * pageblock scanning for freepage moving.
> + *
> + * We didn't actually touch any of the isolated pages, so place them
> + * to the tail of the freelist. This is an optimization for memory
> + * onlining - just onlined memory won't immediately be considered for
> + * allocation.
> */
> if (!isolated_page) {
> - nr_pages = move_freepages_block(zone, page, migratetype, NULL);
> + nr_pages = move_freepages_block(zone, page, migratetype, true,
> + NULL);
> __mod_zone_freepage_state(zone, nr_pages, migratetype);
> }
> set_pageblock_migratetype(page, migratetype);
> --
> 2.26.2

--
Michal Hocko
SUSE Labs