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Commit 4dc4b3d9 authored by KOSAKI Motohiro's avatar KOSAKI Motohiro Committed by Linus Torvalds
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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: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: default avatarMinchan Kim <minchan.kim@gmail.com>
Acked-by: default avatarChristoph Lameter <cl@linux-foundation.org>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus 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