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SubjectRe: [PATCH v2 2/2] vmscan: shrink_slab() require number of lru_pages, not page order
Date
> On Thu, Jul 8, 2010 at 4:40 PM, KOSAKI Motohiro
> <kosaki.motohiro@jp.fujitsu.com> wrote:
> > Fix simple argument error. Usually 'order' is very small value than
> > lru_pages. then it can makes unnecessary icache dropping.
> >
> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
>
> With your test result, This patch makes sense to me.
> Please, include your test result in description.

How's this?

==============================================================
From 19872d74875e2331cbe7eca46c8ef65f5f00d7c4 Mon Sep 17 00:00:00 2001
From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Date: Tue, 13 Jul 2010 13:39:11 +0900
Subject: [PATCH] vmscan: shrink_slab() require number of lru_pages, not page order

Now, shrink_slab() has 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)

Then, 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 makes
bad result.

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.

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>
---
mm/vmscan.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 6ff51c0..1bf9f72 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2612,6 +2612,8 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)

nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
if (nr_slab_pages0 > zone->min_slab_pages) {
+ unsigned long lru_pages = zone_reclaimable_pages(zone);
+
/*
* shrink_slab() does not currently allow us to determine how
* many pages were freed in this zone. So we take the current
@@ -2622,7 +2624,7 @@ 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) &&
+ while (shrink_slab(sc.nr_scanned, gfp_mask, lru_pages) &&
(zone_page_state(zone, NR_SLAB_RECLAIMABLE) + nr_pages >
nr_slab_pages0))
;
--
1.6.5.2





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