Commit 8446b59b authored by Eric Dumazet's avatar Eric Dumazet Committed by Linus Torvalds
Browse files

mm/page_alloc.c: do not acquire zone lock in is_free_buddy_page() 

Grabbing zone lock in is_free_buddy_page() gives a wrong sense of
safety, and has potential performance implications when zone is
experiencing lock contention.

In any case, if a caller needs a stable result, it should grab zone lock
before calling this function.

Link: https://lkml.kernel.org/r/20210922152833.4023972-1-eric.dumazet@gmail.com


Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarHugh Dickins <hughd@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ebeac3ea

mm/page_alloc.c

+5 −5
Original line number Diff line number Diff line
@@ -9356,21 +9356,21 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) 
}

#endif



/*

 * This function returns a stable result only if called under zone lock.

 */

bool is_free_buddy_page(struct page *page)

{

	struct zone *zone = page_zone(page);

	unsigned long pfn = page_to_pfn(page);

	unsigned long flags;

	unsigned int order;



	spin_lock_irqsave(&zone->lock, flags);

	for (order = 0; order < MAX_ORDER; order++) {

		struct page *page_head = page - (pfn & ((1 << order) - 1));



		if (PageBuddy(page_head) && buddy_order(page_head) >= order)

		if (PageBuddy(page_head) &&

		    buddy_order_unsafe(page_head) >= order)

			break;

	}

	spin_unlock_irqrestore(&zone->lock, flags);



	return order < MAX_ORDER;

}