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Commit 56afe477 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
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mm: munlock: bypass per-cpu pvec for putback_lru_page 



After introducing batching by pagevecs into munlock_vma_range(), we can
further improve performance by bypassing the copying into per-cpu pagevec
and the get_page/put_page pair associated with that.  Instead we perform
LRU putback directly from our pagevec.  However, this is possible only for
single-mapped pages that are evictable after munlock.  Unevictable pages
require rechecking after putting on the unevictable list, so for those we
fallback to putback_lru_page(), hich handles that.

After this patch, a 13% speedup was measured for munlocking a 56GB large
memory area with THP disabled.

[akpm@linux-foundation.org:clarify comment]
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarJörn Engel <joern@logfs.org>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Cc: Michel Lespinasse <walken@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1ebb7cc6

mm/mlock.c

+69 −4
Original line number Diff line number Diff line
@@ -226,6 +226,52 @@ static int __mlock_posix_error_return(long retval) 
	return retval;

}



/*

 * Prepare page for fast batched LRU putback via putback_lru_evictable_pagevec()

 *

 * The fast path is available only for evictable pages with single mapping.

 * Then we can bypass the per-cpu pvec and get better performance.

 * when mapcount > 1 we need try_to_munlock() which can fail.

 * when !page_evictable(), we need the full redo logic of putback_lru_page to

 * avoid leaving evictable page in unevictable list.

 *

 * In case of success, @page is added to @pvec and @pgrescued is incremented

 * in case that the page was previously unevictable. @page is also unlocked.

 */

static bool __putback_lru_fast_prepare(struct page *page, struct pagevec *pvec,

		int *pgrescued)

{

	VM_BUG_ON(PageLRU(page));

	VM_BUG_ON(!PageLocked(page));



	if (page_mapcount(page) <= 1 && page_evictable(page)) {

		pagevec_add(pvec, page);

		if (TestClearPageUnevictable(page))

			(*pgrescued)++;

		unlock_page(page);

		return true;

	}



	return false;

}



/*

 * Putback multiple evictable pages to the LRU

 *

 * Batched putback of evictable pages that bypasses the per-cpu pvec. Some of

 * the pages might have meanwhile become unevictable but that is OK.

 */

static void __putback_lru_fast(struct pagevec *pvec, int pgrescued)

{

	count_vm_events(UNEVICTABLE_PGMUNLOCKED, pagevec_count(pvec));

	/*

	 *__pagevec_lru_add() calls release_pages() so we don't call

	 * put_page() explicitly

	 */

	__pagevec_lru_add(pvec);

	count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);

}



/*

 * Munlock a batch of pages from the same zone

 *
@@ -242,6 +288,8 @@ static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone) 
	int i;

	int nr = pagevec_count(pvec);

	int delta_munlocked = -nr;

	struct pagevec pvec_putback;

	int pgrescued = 0;



	/* Phase 1: page isolation */

	spin_lock_irq(&zone->lru_lock);
@@ -279,17 +327,34 @@ skip_munlock: 
	__mod_zone_page_state(zone, NR_MLOCK, delta_munlocked);

	spin_unlock_irq(&zone->lru_lock);



	/* Phase 2: page munlock and putback */

	/* Phase 2: page munlock */

	pagevec_init(&pvec_putback, 0);

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

		struct page *page = pvec->pages[i];



		if (page) {

			lock_page(page);

			if (!__putback_lru_fast_prepare(page, &pvec_putback,

					&pgrescued)) {

				/* Slow path */

				__munlock_isolated_page(page);

				unlock_page(page);

			put_page(page); /* pin from follow_page_mask() */

			}

		}

	}



	/* Phase 3: page putback for pages that qualified for the fast path */

	if (pagevec_count(&pvec_putback))

		__putback_lru_fast(&pvec_putback, pgrescued);



	/* Phase 4: put_page to return pin from follow_page_mask() */

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

		struct page *page = pvec->pages[i];



		if (page)

			put_page(page);

	}



	pagevec_reinit(pvec);

}