linux-kernel - [PATCH 2/2] mm, vmscan: do not overestimate anonymous reclaimable pages

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Date:	Tue, 24 Nov 2015 12:55:00 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
	<linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>
Subject: [PATCH 2/2] mm, vmscan: do not overestimate anonymous reclaimable pages

From: Michal Hocko <mhocko@...e.com>

zone_reclaimable_pages considers all anonymous pages on LRUs reclaimable
if there is at least one entry on the swap storage left. This can be
really misleading when the swap is short on space and skew reclaim
decisions based on zone_reclaimable_pages. Fix this by clamping the
number to the minimum of the available swap space and anon LRU pages.

Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 mm/vmscan.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 946d348f5040..646001a1f279 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -195,15 +195,20 @@ static bool sane_reclaim(struct scan_control *sc)
 static unsigned long zone_reclaimable_pages(struct zone *zone)
 {
 	unsigned long nr;
+	long nr_swap = get_nr_swap_pages();
 
 	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
 	     zone_page_state(zone, NR_INACTIVE_FILE) +
 	     zone_page_state(zone, NR_ISOLATED_FILE);
 
-	if (get_nr_swap_pages() > 0)
-		nr += zone_page_state(zone, NR_ACTIVE_ANON) +
-		      zone_page_state(zone, NR_INACTIVE_ANON) +
-		      zone_page_state(zone, NR_ISOLATED_ANON);
+	if (nr_swap > 0) {
+		unsigned long anon;
+
+		anon = zone_page_state(zone, NR_ACTIVE_ANON) +
+		       zone_page_state(zone, NR_INACTIVE_ANON) +
+		       zone_page_state(zone, NR_ISOLATED_ANON);
+		nr += min_t(unsigned long, nr_swap, anon);
+	}
 
 	return nr;
 }
-- 
2.6.2

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