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

Wei Yang
2020-09-29T09:18:20Z

On Mon, Sep 28, 2020 at 08:21:08PM +0200, 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.
>
>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]);
>+}
>+

Would it be better to pass the *to_tail* to move_to_free_list(), so we won't
have a new function?

> 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);

And here, we just need to pass the *to_tail* to move_to_free_list().

> 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

Others looks good to me.

--
Wei Yang
Help you, Help me