From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752270AbdFAP6n (ORCPT ); Thu, 1 Jun 2017 11:58:43 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:33778 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752287AbdFAPpQ (ORCPT ); Thu, 1 Jun 2017 11:45:16 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Vinayak Menon" , "Linus Torvalds" , "Mel Gorman" , "Michal Hocko" , "Anton Vorontsov" , "Minchan Kim" , "Shiraz Hashim" , "Vlastimil Babka" , "Johannes Weiner" , "Rik van Riel" , "Vladimir Davydov" Date: Thu, 01 Jun 2017 16:43:16 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 166/212] mm: vmpressure: fix sending wrong events on underflow In-Reply-To: X-SA-Exim-Connect-IP: 82.70.136.246 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.44-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Vinayak Menon 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 Acked-by: Minchan Kim Acked-by: Michal Hocko Cc: Johannes Weiner Cc: Mel Gorman Cc: Vlastimil Babka Cc: Rik van Riel Cc: Vladimir Davydov Cc: Anton Vorontsov Cc: Shiraz Hashim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Ben Hutchings --- 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);