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    SubjectRe: [PATCH RFC 3/4] mm/page_alloc: always move pages to the tail of the freelist in unset_migratetype_isolate()
    On Wed, Sep 16, 2020 at 08:34:10PM +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.
    >
    >This change results in all pages getting onlined via online_pages() to
    >be placed to the tail of the freelist.

    I am sorry to not follow again. unset_migratetype_isolate() is used in
    __offline_pages if my understanding is correct. How does it contribute on
    online_pages?

    >
    >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 | 2 ++
    > mm/page_alloc.c | 36 +++++++++++++++++++++++++++++-----
    > mm/page_isolation.c | 8 ++++++--
    > 3 files changed, 39 insertions(+), 7 deletions(-)
    >
    >diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
    >index 572458016331..a36be2cf4dbb 100644
    >--- a/include/linux/page-isolation.h
    >+++ b/include/linux/page-isolation.h
    >@@ -38,6 +38,8 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
    > 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_tail(struct zone *zone, struct page *page,
    >+ int migratetype);
    >
    > /*
    > * 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 bba9a0f60c70..75b0f49b4022 100644
    >--- a/mm/page_alloc.c
    >+++ b/mm/page_alloc.c
    >@@ -899,6 +899,15 @@ 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)
    > {
    >@@ -2323,7 +2332,7 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
    > */
    > static int move_freepages(struct zone *zone,
    > struct page *start_page, struct page *end_page,
    >- int migratetype, int *num_movable)
    >+ int migratetype, int *num_movable, bool to_tail)
    > {
    > struct page *page;
    > unsigned int order;
    >@@ -2354,7 +2363,10 @@ 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;
    > }
    >@@ -2362,8 +2374,9 @@ 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)
    >+static int __move_freepages_block(struct zone *zone, struct page *page,
    >+ int migratetype, int *num_movable,
    >+ bool to_tail)
    > {
    > unsigned long start_pfn, end_pfn;
    > struct page *start_page, *end_page;
    >@@ -2384,7 +2397,20 @@ int move_freepages_block(struct zone *zone, struct page *page,
    > return 0;
    >
    > return move_freepages(zone, start_page, end_page, migratetype,
    >- num_movable);
    >+ num_movable, to_tail);
    >+}
    >+
    >+int move_freepages_block(struct zone *zone, struct page *page,
    >+ int migratetype, int *num_movable)
    >+{
    >+ return __move_freepages_block(zone, page, migratetype, num_movable,
    >+ false);
    >+}
    >+
    >+int move_freepages_block_tail(struct zone *zone, struct page *page,
    >+ int migratetype)
    >+{
    >+ return __move_freepages_block(zone, page, migratetype, NULL, true);
    > }
    >
    > static void change_pageblock_range(struct page *pageblock_page,
    >diff --git a/mm/page_isolation.c b/mm/page_isolation.c
    >index abfe26ad59fd..84aa1d14751d 100644
    >--- a/mm/page_isolation.c
    >+++ b/mm/page_isolation.c
    >@@ -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 +106,13 @@ 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 freelists. This is especially relevant during
    >+ * memory onlining.
    > */
    > if (!isolated_page) {
    >- nr_pages = move_freepages_block(zone, page, migratetype, NULL);
    >+ nr_pages = move_freepages_block_tail(zone, page, migratetype);
    > __mod_zone_freepage_state(zone, nr_pages, migratetype);
    > }
    > set_pageblock_migratetype(page, migratetype);
    >--
    >2.26.2

    --
    Wei Yang
    Help you, Help me

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