Messages in this thread Patch in this message | | | From | Vinayak Menon <> | Subject | [PATCH 2/2 RESEND] mm: vmpressure: fix sending wrong events on underflow | Date | Mon, 6 Feb 2017 17:54:10 +0530 |
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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@kernel.org> Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org> --- mm/vmpressure.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/mm/vmpressure.c b/mm/vmpressure.c index 149fdf6..3281b34 100644 --- a/mm/vmpressure.c +++ b/mm/vmpressure.c @@ -112,8 +112,10 @@ 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; + 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 @@ -124,6 +126,7 @@ 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); -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation
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