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Message-Id: <591152d8215c0ef63ac57aa8e57a6c894a5a4259.1489497268.git.jslaby@suse.cz>
Date: Tue, 14 Mar 2017 14:15:09 +0100
From: Jiri Slaby <jslaby@...e.cz>
To: stable@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
Vinayak Menon <vinmenon@...eaurora.org>,
Johannes Weiner <hannes@...xchg.org>,
Mel Gorman <mgorman@...hsingularity.net>,
Vlastimil Babka <vbabka@...e.cz>,
Rik van Riel <riel@...hat.com>,
Vladimir Davydov <vdavydov.dev@...il.com>,
Anton Vorontsov <anton.vorontsov@...aro.org>,
Shiraz Hashim <shashim@...eaurora.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 18/60] mm: vmpressure: fix sending wrong events on underflow
From: Vinayak Menon <vinmenon@...eaurora.org>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit e1587a4945408faa58d0485002c110eb2454740c upstream.
At the end of a window period, if the reclaimed pages is greater than
scanned, an unsigned underflow can result in a huge pressure value and
thus a critical event. Reclaimed pages is found to go higher than
scanned because of the addition of reclaimed slab pages to reclaimed in
shrink_node without a corresponding increment to scanned pages.
Minchan Kim mentioned that this can also happen in the case of a THP
page where the scanned is 1 and reclaimed could be 512.
Link: http://lkml.kernel.org/r/1486641577-11685-1-git-send-email-vinmenon@codeaurora.org
Signed-off-by: Vinayak Menon <vinmenon@...eaurora.org>
Acked-by: Minchan Kim <minchan@...nel.org>
Acked-by: Michal Hocko <mhocko@...e.com>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Rik van Riel <riel@...hat.com>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>
Cc: Anton Vorontsov <anton.vorontsov@...aro.org>
Cc: Shiraz Hashim <shashim@...eaurora.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
mm/vmpressure.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index c98b14ee69d6..7ef7172d44f8 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -111,9 +111,16 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
unsigned long reclaimed)
{
unsigned long scale = scanned + reclaimed;
- unsigned long pressure;
+ unsigned long pressure = 0;
/*
+ * reclaimed can be greater than scanned in cases
+ * like THP, where the scanned is 1 and reclaimed
+ * could be 512
+ */
+ if (reclaimed >= scanned)
+ goto out;
+ /*
* 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
@@ -123,6 +130,7 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
pressure = scale - (reclaimed * scale / scanned);
pressure = pressure * 100 / scale;
+out:
pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__, pressure,
scanned, reclaimed);
--
2.12.0
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