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mm: vmpressure: fix sending wrong events on underflow 

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@codeaurora.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Michal 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
This commit is contained in:
Vinayak Menon 2017-02-24 14:59:39 -08:00 committed by syphyr
parent 80680c787d
commit b32eb3e65f
1 changed files with 9 additions and 1 deletions
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10
mm/vmpressure.c
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@ -158,8 +158,15 @@ static unsigned long vmpressure_calc_pressure(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
@ -170,6 +177,7 @@ static unsigned long vmpressure_calc_pressure(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);