Messages in this thread | | | Date | Mon, 17 Dec 2007 10:44:53 +0000 | From | Mel Gorman <> | Subject | Re: [RFC] move free page back to MIGRATE_MOVABLE? |
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On (13/12/07 13:19), Shaohua Li didst pronounce: > pages are MIGRATE_MOVABLE initially, and fallback to other types. If the > pages are freed, I wonder why not move them back to MIGRATE_MOVABLE.
Because there is no need, if a MIGRATE_MOVABLE allocation needs more pages, they will be acquired during fallback which always steals the largest block. Lets say that a MIGRATE_UNMOVABLE block is freed and it is larger than pageblock_order. The next MIGRATE_MOVABLE allocation will find it during fallback if necessary.
> This, for example, can help memory remove. >
I don't see how. When hot-removing, MIGRATE_MOVABLE blocks are considered possible to remove but they are also considered movable if the pages are free.
> Thanks, > Shaohua > > Index: linux/mm/page_alloc.c > =================================================================== > --- linux.orig/mm/page_alloc.c 2007-12-13 11:44:36.000000000 +0800 > +++ linux/mm/page_alloc.c 2007-12-13 12:04:59.000000000 +0800 > @@ -386,6 +386,9 @@ static inline int page_is_buddy(struct p > return 0; > } > > +int move_freepages(struct zone *zone, > + struct page *start_page, struct page *end_page, > + int migratetype); > /* > * Freeing function for a buddy system allocator. > * > @@ -446,6 +449,17 @@ static inline void __free_one_page(struc > list_add(&page->lru, > &zone->free_area[order].free_list[migratetype]); > zone->free_area[order].nr_free++; > + > + if (order >= pageblock_order && migratetype != MIGRATE_MOVABLE) { > + struct page *tmp = page; > + > + move_freepages(zone, page, page + (1 << order) - 1, MIGRATE_MOVABLE); > +
This is unnecessary and affects a commonly used path. If a MOVABLE allocation needs more pages later, it will find the large free block during fallback.
> + while (tmp < page + (1 << order)) { > + set_pageblock_migratetype(tmp, MIGRATE_MOVABLE); > + tmp += pageblock_nr_pages; > + } > + } > } > > static inline int free_pages_check(struct page *page) >
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
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