Commit d34c5fa0 authored Jun 04, 2014 by Mel Gorman Committed by Linus Torvalds Jun 04, 2014

mm: page_alloc: only check the zone id check if pages are buddies



A node/zone index is used to check if pages are compatible for merging
but this happens unconditionally even if the buddy page is not free. Defer
the calculation as long as possible. Ideally we would check the zone boundary
but nodes can overlap.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Jan Kara <jack@suse.cz>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 664eedde

mm/page_alloc.c

+13 −3

Original line number	Diff line number	Diff line
		@@ -509,16 +509,26 @@ static inline int page_is_buddy(struct page page, struct page buddy,
		if (!pfn_valid_within(page_to_pfn(buddy)))
		return 0;

		if (page_is_guard(buddy) && page_order(buddy) == order) {
		VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);

		if (page_zone_id(page) != page_zone_id(buddy))
		return 0;

		if (page_is_guard(buddy) && page_order(buddy) == order) {
		VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);
		return 1;
		}

		if (PageBuddy(buddy) && page_order(buddy) == order) {
		VM_BUG_ON_PAGE(page_count(buddy) != 0, buddy);

		/*
		* zone check is done late to avoid uselessly
		* calculating zone/node ids for pages that could
		* never merge.
		*/
		if (page_zone_id(page) != page_zone_id(buddy))
		return 0;

		return 1;
		}
		return 0;

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