Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753054AbdFSSfc (ORCPT + 2 others); Mon, 19 Jun 2017 14:35:32 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:52073 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753010AbdFSSf3 (ORCPT ); Mon, 19 Jun 2017 14:35:29 -0400 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, linux@roeck-us.net Cc: Vinayak Menon , Johannes Weiner , Mel Gorman , Vlastimil Babka , Rik van Riel , Vladimir Davydov , Anton Vorontsov , Shiraz Hashim , Andrew Morton , Linus Torvalds , Willy Tarreau Subject: [PATCH 3.10 155/268] mm: vmpressure: fix sending wrong events on underflow Date: Mon, 19 Jun 2017 20:30:54 +0200 Message-Id: <1497897167-14556-156-git-send-email-w@1wt.eu> X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a In-Reply-To: <1497897167-14556-1-git-send-email-w@1wt.eu> References: <1497897167-14556-1-git-send-email-w@1wt.eu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: 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: Willy Tarreau --- mm/vmpressure.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/vmpressure.c b/mm/vmpressure.c index 736a601..e8955f9 100644 --- a/mm/vmpressure.c +++ b/mm/vmpressure.c @@ -116,9 +116,16 @@ 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 * time is in VM reclaimer's "ticks", i.e. number of pages @@ -128,6 +135,7 @@ 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); -- 2.8.0.rc2.1.gbe9624a