Commit 4dc4b3d9 authored Aug 09, 2010 by KOSAKI Motohiro Committed by Linus Torvalds Aug 09, 2010

vmscan: shrink_slab() requires the number of lru_pages, not the page order



Presently shrink_slab() has the following scanning equation.

                            lru_scanned        max_pass
  basic_scan_objects = 4 x -------------  x -----------------------------
                            lru_pages        shrinker->seeks (default:2)

  scan_objects = min(basic_scan_objects, max_pass * 2)

If we pass very small value as lru_pages instead real number of lru pages,
shrink_slab() drop much objects rather than necessary.  And now,
__zone_reclaim() pass 'order' as lru_pages by mistake.  That produces a
bad result.

For example, if we receive very low memory pressure (scan = 32, order =
0), shrink_slab() via zone_reclaim() always drop _all_ icache/dcache
objects.  (see above equation, very small lru_pages make very big
scan_objects result).

This patch fixes it.

[akpm@linux-foundation.org: fix layout, typos]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: Christoph Lameter <cl@linux-foundation.org>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 57250a5b

mm/vmscan.c

+13 −4

Original line number	Diff line number	Diff line
		@@ -2635,10 +2635,19 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
		* Note that shrink_slab will free memory on all zones and may
		* take a long time.
		*/
		while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
		(zone_page_state(zone, NR_SLAB_RECLAIMABLE) + nr_pages >
		nr_slab_pages0))
		;
		for (;;) {
		unsigned long lru_pages = zone_reclaimable_pages(zone);

		/* No reclaimable slab or very low memory pressure */
		if (!shrink_slab(sc.nr_scanned, gfp_mask, lru_pages))
		break;

		/* Freed enough memory */
		nr_slab_pages1 = zone_page_state(zone,
		NR_SLAB_RECLAIMABLE);
		if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
		break;
		}

		/*
		* Update nr_reclaimed by the number of slab pages we

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