4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Vinayak Menon <[email protected]> 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/[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]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- 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);
