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authorVinayak Menon <[email protected]>2017-02-24 14:59:39 -0800
committerLinus Torvalds <[email protected]>2017-02-24 17:46:56 -0800
commite1587a4945408faa58d0485002c110eb2454740c (patch)
tree83aca8da303ea0e1001aca318de83885a140d881
parent3a4f8a0b3ffa733ffbb327685e83b63383127cf6 (diff)
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. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Vinayak Menon <[email protected]> Acked-by: Minchan Kim <[email protected]> Acked-by: Michal Hocko <[email protected]> Cc: Johannes Weiner <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Vlastimil Babka <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Vladimir Davydov <[email protected]> Cc: Anton Vorontsov <[email protected]> Cc: Shiraz Hashim <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
-rw-r--r--mm/vmpressure.c10
1 files changed, 9 insertions, 1 deletions
diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index 149fdf6c5c56..6063581f705c 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);