From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id A99A06B0253 for ; Fri, 27 Jan 2017 03:14:26 -0500 (EST) Received: by mail-pf0-f198.google.com with SMTP id 80so340478085pfy.2 for ; Fri, 27 Jan 2017 00:14:26 -0800 (PST) Received: from smtp.codeaurora.org (smtp.codeaurora.org. [198.145.29.96]) by mx.google.com with ESMTPS id s19si3752251pfd.78.2017.01.27.00.14.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 27 Jan 2017 00:14:25 -0800 (PST) From: 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> In-Reply-To: <1485504817-3124-1-git-send-email-vinmenon@codeaurora.org> References: <1485504817-3124-1-git-send-email-vinmenon@codeaurora.org> Sender: owner-linux-mm@kvack.org List-ID: 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 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org