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>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a3d669f..9789a2c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2635,10 +2635,19 @@
* 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
