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From: Hyunhee Kim <hyunhee.kim@samsung.com>
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Subject: [PATCH v2] vmpressure: consider "scanned < reclaimed" case when
 calculating  a pressure level.
Date: Thu, 27 Jun 2013 15:12:10 +0900
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Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: 'Michal Hocko' <mhocko@suse.cz>, 'Anton Vorontsov' <anton@enomsg.org>, linux-mm@kvack.org, akpm@linux-foundation.org, rob@landley.net, kamezawa.hiroyu@jp.fujitsu.com, hannes@cmpxchg.org, rientjes@google.com, kirill@shutemov.name, 'Kyungmin Park' <kyungmin.park@samsung.com>, 'Minchan Kim' <minchan@kernel.org>

In vmpressure, the pressure level is calculated based on the ratio
of how many pages were scanned vs. reclaimed in a given time window.
However, there is a possibility that "scanned < reclaimed" in such a
case, when reclaiming ends by fatal signal in shrink_inactive_list.
So, with this patch, we just return "low" level when "scanned < reclaimed"
happens not to have userland miss reclaim activity.

Signed-off-by: Hyunhee Kim <hyunhee.kim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
---
 mm/vmpressure.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index 736a601..8c60cad 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -119,6 +119,14 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
 	unsigned long pressure;
 
 	/*
+	 * This could happen, in such a case, when reclaiming ends by fatal
+	 * signal in shrink_inactive_list(). In this case, return
+	 * VMPRESSURE_LOW not to have userland miss reclaim activity.
+	 */
+	if (reclaimed > scanned)
+		return VMPRESSURE_LOW;
+
+	/*
 	 * We calculate the ratio (in percents) of how many pages were
 	 * scanned vs. reclaimed in a given time frame (window). Note that
 	 * time is in VM reclaimer's "ticks", i.e. number of pages
-- 
1.7.9.5


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