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Message-Id: <1486641577-11685-1-git-send-email-vinmenon@codeaurora.org>
Date: Thu, 9 Feb 2017 17:29:36 +0530
From: Vinayak Menon <vinmenon@...eaurora.org>
To: akpm@...ux-foundation.org, hannes@...xchg.org,
mgorman@...hsingularity.net, vbabka@...e.cz, mhocko@...e.com,
riel@...hat.com, vdavydov.dev@...il.com,
anton.vorontsov@...aro.org, minchan@...nel.org,
shashim@...eaurora.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Vinayak Menon <vinmenon@...eaurora.org>
Subject: [PATCH 1/2 v2] mm: vmpressure: fix sending wrong events on underflow
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.
Acked-by: Minchan Kim <minchan@...nel.org>
Signed-off-by: Vinayak Menon <vinmenon@...eaurora.org>
---
v2: Adding a comment and reordering the patches
as per Michal's suggestion
mm/vmpressure.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index 149fdf6..6063581 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -112,9 +112,16 @@ 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
@@ -124,6 +131,7 @@ 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);
--
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