Re: [PATCH RFC 3/4] mm/page_alloc: always move pages to the tail of the freelist in unset_migratetype_isolate()

Wei Yang
2020-09-25T02:45:59Z

On Thu, Sep 24, 2020 at 01:13:29PM +0200, Vlastimil Babka wrote:
>On 9/16/20 8:34 PM, 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.
>>
>> 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]);
>> +}
>
>There are just 3 callers of move_to_free_list() before this patch, I would just
>add the to_tail parameter there instead of new wrapper. For callers with
>constant parameter, the inline will eliminate it anyway.

Got the same feeling :-)

>
>> 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);
>> }
>
>Likewise, just 5 callers of move_freepages_block(), all in the files you're
>already changing, so no need for this wrappers IMHO.
>
>Thanks,
>Vlastimil
>
>> 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);
>>

--
Wei Yang
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