Commit 46453a6e authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

[PATCH] mm: never ClearPageLRU released pages 



If vmscan finds a zero refcount page on the lru list, never ClearPageLRU
it.  This means the release code need not hold ->lru_lock to stabilise
PageLRU, so that lock may be skipped entirely when releasing !PageLRU pages
(because we know PageLRU won't have been temporarily cleared by vmscan,
which was previously guaranteed by holding the lock to synchronise against
vmscan).

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 2492ecc1

mm/swap.c

+27 −25
Original line number Diff line number Diff line
@@ -209,19 +209,18 @@ int lru_add_drain_all(void) 
 */

void fastcall __page_cache_release(struct page *page)

{

	if (PageLRU(page)) {

		unsigned long flags;

		struct zone *zone = page_zone(page);



		spin_lock_irqsave(&zone->lru_lock, flags);

	if (TestClearPageLRU(page))

		if (!TestClearPageLRU(page))

			BUG();

		del_page_from_lru(zone, page);

	if (page_count(page) != 0)

		page = NULL;

		spin_unlock_irqrestore(&zone->lru_lock, flags);

	if (page)

	}

	free_hot_page(page);

}



EXPORT_SYMBOL(__page_cache_release);



/*
@@ -245,7 +244,6 @@ void release_pages(struct page **pages, int nr, int cold) 
	pagevec_init(&pages_to_free, cold);

	for (i = 0; i < nr; i++) {

		struct page *page = pages[i];

		struct zone *pagezone;



		if (unlikely(PageCompound(page))) {

			if (zone) {
@@ -259,22 +257,26 @@ void release_pages(struct page **pages, int nr, int cold) 
		if (!put_page_testzero(page))

			continue;



		pagezone = page_zone(page);

		if (PageLRU(page)) {

			struct zone *pagezone = page_zone(page);

			if (pagezone != zone) {

				if (zone)

					spin_unlock_irq(&zone->lru_lock);

				zone = pagezone;

				spin_lock_irq(&zone->lru_lock);

			}

		if (TestClearPageLRU(page))

			if (!TestClearPageLRU(page))

				BUG();

			del_page_from_lru(zone, page);

		if (page_count(page) == 0) {

		}



		if (!pagevec_add(&pages_to_free, page)) {

			if (zone) {

				spin_unlock_irq(&zone->lru_lock);

				zone = NULL;

			}

			__pagevec_free(&pages_to_free);

			pagevec_reinit(&pages_to_free);

				zone = NULL;	/* No lock is held */

			}

  		}

	}

	if (zone)

mm/vmscan.c

+11 −7
Original line number Diff line number Diff line
@@ -1085,22 +1085,26 @@ static int isolate_lru_pages(int nr_to_scan, struct list_head *src, 
		page = lru_to_page(src);

		prefetchw_prev_lru_page(page, src, flags);



		if (!TestClearPageLRU(page))

			BUG();

		list_del(&page->lru);

		if (get_page_testone(page)) {

		if (unlikely(get_page_testone(page))) {

			/*

			 * It is being freed elsewhere

			 */

			__put_page(page);

			SetPageLRU(page);

			list_add(&page->lru, src);

			continue;

		} else {

		}



		/*

		 * Be careful not to clear PageLRU until after we're sure

		 * the page is not being freed elsewhere -- the page release

		 * code relies on it.

		 */

		if (!TestClearPageLRU(page))

			BUG();

		list_add(&page->lru, dst);

		nr_taken++;

	}

	}



	*scanned = scan;

	return nr_taken;

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