From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754509AbdA0IPY (ORCPT ); Fri, 27 Jan 2017 03:15:24 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:33908 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754261AbdA0IO1 (ORCPT ); Fri, 27 Jan 2017 03:14:27 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 9B4BD609C6 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=vinmenon@codeaurora.org From: Vinayak Menon To: akpm@linux-foundation.org, hannes@cmpxchg.org, mgorman@techsingularity.net, vbabka@suse.cz, mhocko@suse.com, riel@redhat.com, vdavydov.dev@gmail.com, anton.vorontsov@linaro.org, minchan@kernel.org, shashim@codeaurora.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vinayak Menon Subject: [PATCH 2/2] mm: vmpressure: fix sending wrong events on underflow Date: Fri, 27 Jan 2017 13:43:37 +0530 Message-Id: <1485504817-3124-2-git-send-email-vinmenon@codeaurora.org> X-Mailer: git-send-email 1.8.2.1 In-Reply-To: <1485504817-3124-1-git-send-email-vinmenon@codeaurora.org> References: <1485504817-3124-1-git-send-email-vinmenon@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Signed-off-by: Vinayak Menon --- mm/vmpressure.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/vmpressure.c b/mm/vmpressure.c index 149fdf6..3281b34 100644 --- a/mm/vmpressure.c +++ b/mm/vmpressure.c @@ -112,8 +112,10 @@ 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; + 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 @@ -124,6 +126,7 @@ 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); -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation