From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B36F4C282C2 for ; Wed, 13 Feb 2019 14:32:04 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 79D32222B2 for ; Wed, 13 Feb 2019 14:32:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 79D32222B2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4A0CC8E0002; Wed, 13 Feb 2019 09:32:03 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 44DB48E0001; Wed, 13 Feb 2019 09:32:03 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 365DD8E0002; Wed, 13 Feb 2019 09:32:03 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id CF08B8E0001 for ; Wed, 13 Feb 2019 09:32:02 -0500 (EST) Received: by mail-ed1-f70.google.com with SMTP id p52so1062008eda.18 for ; Wed, 13 Feb 2019 06:32:02 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-original-authentication-results:x-gm-message-state:subject:to:cc :references:from:message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=8thNn5EfuxKMLdeorsfdk3C0LS7LMekDdHKYDhSQPQY=; b=hqIBjxRw02Hu5kYcsLTiCzXkR/1hUb7YjVbPzgL4lbqYpruz+0d/9fn14t8NyGmpj3 ydC1LJKz60ULbwL5cEVYXvnBQV3kH29dnlB1fBRZM+7JKpa2uWdKG9eNT06CxiPHoiTz H5L/SRFDbaRqgRpAxuhzAZ0m1PFmGTHmEobejvFdcTLPTBWMeGMyAPzAb5ono7PpZTua WE7H16DSWX5Qjb+ko9nQBUFI8lbgozg6FkwP2MFoFO5iecGBvVTkaOZHT7jejzty8cHO Zoh2jomiOWJ5aJhI4t8cM7XIVgmbOF3qXqvaq6eZ25NM/tSBA0dfwBbM/YVOG+APQ6dk uZPg== X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Gm-Message-State: AHQUAubAU/4xBjCcCP+gMTWifO/QGf629gmo1owa/DrLJj0fWJXzhxjs 2AfszWH9CicE+WqxCPiR+aYcj9YqEEtG65KxKNDfN7AxTQQlei1n22Kxv5I2cgzpZr7M30EgySa m1VUHMxd3ec1ekYUl/UO6sK7LfKCGZD/qGLEd79ynY9fCbdGFk7Fni8ZoynpkN/QQ3A== X-Received: by 2002:a50:cf41:: with SMTP id d1mr648212edk.242.1550068322390; Wed, 13 Feb 2019 06:32:02 -0800 (PST) X-Google-Smtp-Source: AHgI3IY/fEvUmf6Lx6MAqJvvsMOFdiOK0fsiu2R/ESSzY4Xdd8CJHh/n33Z7OqRLGWFGMrMsA+AF X-Received: by 2002:a50:cf41:: with SMTP id d1mr648164edk.242.1550068321578; Wed, 13 Feb 2019 06:32:01 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1550068321; cv=none; d=google.com; s=arc-20160816; b=xKN45yblCLFL6OSOAoaoHhXDo60NxNy7CkrRDkeWJfB5cvuyPC/V/xlgZbAIxmyKs1 Y9OkCMp+Khglw2lEv1k1Q9C8VwGOxjgpuUiDufOBpxEZ4hB/895FfKHG51EqZDXSeUhI nMvVMhL8xAdwVxMFb4aCTBMauPHaBLs/dozN0fihMexN7w8xwSvmokOm9gNqV1iuz3IY cp2aFJOgXdFCze38E/nUVbD+k6Y1rNDfRW0ekYoFFhhb2gfkVHTxXbgVdZmdsvxoyQ47 pcKBfFbClDZEsjI87oSBLCc0HK6XcUBtBMU/JIxeCEvVNMYzana/CTLGAdtObFm+9ApU Qn/w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:references:cc:to:subject; bh=8thNn5EfuxKMLdeorsfdk3C0LS7LMekDdHKYDhSQPQY=; b=OlqupQFlyoltm8vwTLdwRndh2XPd834ksxMKgQsn2JXRpIrUIPspAaPDKcQvF8ZDIh u1WqIX6a6s5zrioTK0p5asd4dC498Wclk/744mvaLcpmuPrOv5Of/mWLTDJbjir303Ms XlomGZ4NafUX0IaH8T3iHK7A04qiawv1A1rheJfenA+jSVSEVaMUWXrBk4/OvyVAQaYT kOF4CFvmwggsovAHhYYSHJ3CEMj3NZfE/f3Pm1KeMUMj5sddFCKj87aRfiPZr4PmB0ey rKp3gh4xT1ra4KFd7XhE7Z/XbOXpCiwZhFP7Lzpn9e60wV51NI64hcf8IZCZxHEOM0fc eBFg== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z7si760728edh.60.2019.02.13.06.32.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 13 Feb 2019 06:32:01 -0800 (PST) Received-SPF: pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id EDC5AAF27; Wed, 13 Feb 2019 14:32:00 +0000 (UTC) Subject: Re: [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks v2 To: Mel Gorman , Andrew Morton Cc: Yury Norov , Andrea Arcangeli , David Rientjes , Michal Hocko , Will Deacon , Catalin Marinas , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org References: <20190213131923.GQ9565@techsingularity.net> <20190213143012.GT9565@techsingularity.net> From: Vlastimil Babka Message-ID: <7c0d323f-cad8-205b-5a8a-60da180a4ed0@suse.cz> Date: Wed, 13 Feb 2019 15:31:59 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190213143012.GT9565@techsingularity.net> Content-Type: text/plain; charset=iso-8859-15 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2/13/19 3:30 PM, Mel Gorman wrote: > Yury Norov reported that an arm64 KVM instance could not boot since after > v5.0-rc1 and could addressed by reverting the patches > > 1c30844d2dfe272d58c ("mm: reclaim small amounts of memory when an external > 73444bc4d8f92e46a20 ("mm, page_alloc: do not wake kswapd with zone lock held") > > The problem is that a division by zero error is possible if boosting > occurs very early in boot if the system has very little memory. This > patch avoids the division by zero error. > > Fixes: 1c30844d2dfe ("mm: reclaim small amounts of memory when an external fragmentation event occurs") > Reported-and-tested-by: Yury Norov > Tested-by: Will Deacon > Signed-off-by: Mel Gorman Acked-by: Vlastimil Babka Thanks, sorry for the noise before. > --- > mm/page_alloc.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index d295c9bc01a8..bb1c7d843ebf 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2170,6 +2170,18 @@ static inline void boost_watermark(struct zone *zone) > > max_boost = mult_frac(zone->_watermark[WMARK_HIGH], > watermark_boost_factor, 10000); > + > + /* > + * high watermark may be uninitialised if fragmentation occurs > + * very early in boot so do not boost. We do not fall > + * through and boost by pageblock_nr_pages as failing > + * allocations that early means that reclaim is not going > + * to help and it may even be impossible to reclaim the > + * boosted watermark resulting in a hang. > + */ > + if (!max_boost) > + return; > + > max_boost = max(pageblock_nr_pages, max_boost); > > zone->watermark_boost = min(zone->watermark_boost + pageblock_nr_pages, >