Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit e1587a49 authored by Vinayak Menon's avatar Vinayak Menon Committed by Linus Torvalds
Browse files

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/1486641577-11685-1-git-send-email-vinmenon@codeaurora.org


Signed-off-by: default avatarVinayak Menon <vinmenon@codeaurora.org>
Acked-by: default avatarMinchan Kim <minchan@kernel.org>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Anton Vorontsov <anton.vorontsov@linaro.org>
Cc: Shiraz Hashim <shashim@codeaurora.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3a4f8a0b

mm/vmpressure.c

+9 −1
Original line number Diff line number Diff line
@@ -112,8 +112,15 @@ 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
@@ -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);