Commit 293ffa5e authored Oct 15, 2020 by David Hildenbrand Committed by Linus Torvalds Oct 16, 2020

mm/page_alloc: move pages to tail in move_to_free_list()



Whenever we move pages between freelists via move_to_free_list()/
move_freepages_block(), we don't actually touch the pages:
1. Page isolation doesn't actually touch the pages, it simply isolates
   pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
   When undoing isolation, we move the pages back to the target list.
2. Page stealing (steal_suitable_fallback()) moves free pages directly
   between lists without touching them.
3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock() moves
   free pages directly between freelists without touching them.

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. To simplify, let's move the
pages to the tail for all move_to_free_list()/move_freepages_block() users.

In 2., the target list is empty, so there should be no change.  In 3., we
might observe a change, however, highatomic is more concerned about
allocations succeeding than cache hotness - if we ever realize this change
degrades a workload, we can special-case this instance and add a proper
comment.

This change results in all pages getting onlined via online_pages() to be
placed to the tail of the freelist.

Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Scott Cheloha <cheloha@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Link: https://lkml.kernel.org/r/20201005121534.15649-4-david@redhat.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 47b6a24a

mm/page_alloc.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -901,13 +901,17 @@ static inline void add_to_free_list_tail(struct page page, struct zone zone,
		area->nr_free++;
		}

		/* Used for pages which are on another list */
		/*
		* Used for pages which are on another list. Move the pages to the tail
		* of the list - so the moved pages won't immediately be considered for
		* allocation again (e.g., optimization for memory onlining).
		*/
		static inline void move_to_free_list(struct page page, struct zone zone,
		unsigned int order, int migratetype)
		{
		struct free_area *area = &zone->free_area[order];

		list_move(&page->lru, &area->free_list[migratetype]);
		list_move_tail(&page->lru, &area->free_list[migratetype]);
		}

		static inline void del_page_from_free_list(struct page page, struct zone zone,
		@@ -2340,7 +2344,7 @@ static inline struct page __rmqueue_cma_fallback(struct zone zone,
		#endif

		/*
		* Move the free pages in a range to the free lists of the requested type.
		* Move the free pages in a range to the freelist tail of the requested type.
		* Note that start_page and end_pages are not aligned on a pageblock
		* boundary. If alignment is required, use move_freepages_block()
		*/

mm/page_isolation.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -106,6 +106,11 @@ 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);

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