4.10-stable review patch. If anyone has any objections, please let me know.
------------------ From: Vinayak Menon <vinme...@codeaurora.org> 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-vinme...@codeaurora.org Signed-off-by: Vinayak Menon <vinme...@codeaurora.org> Acked-by: Minchan Kim <minc...@kernel.org> Acked-by: Michal Hocko <mho...@suse.com> Cc: Johannes Weiner <han...@cmpxchg.org> Cc: Mel Gorman <mgor...@techsingularity.net> Cc: Vlastimil Babka <vba...@suse.cz> Cc: Rik van Riel <r...@redhat.com> Cc: Vladimir Davydov <vdavydov....@gmail.com> Cc: Anton Vorontsov <anton.voront...@linaro.org> Cc: Shiraz Hashim <shas...@codeaurora.org> Signed-off-by: Andrew Morton <a...@linux-foundation.org> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- mm/vmpressure.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- a/mm/vmpressure.c +++ b/mm/vmpressure.c @@ -112,9 +112,16 @@ static enum vmpressure_levels vmpressure 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 pressure = scale - (reclaimed * scale / scanned); pressure = pressure * 100 / scale; +out: pr_debug("%s: %3lu (s: %lu r: %lu)\n", __func__, pressure, scanned, reclaimed);
