From patchwork Wed Feb 13 13:19:23 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mel Gorman X-Patchwork-Id: 10809727 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 7F89917E0 for ; Wed, 13 Feb 2019 13:19:58 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 69FB12CDA4 for ; Wed, 13 Feb 2019 13:19:58 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 5E5A02CDA9; Wed, 13 Feb 2019 13:19:58 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 0FC1C2CDA4 for ; Wed, 13 Feb 2019 13:19:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:Message-ID:Subject:To:From :Date:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References: List-Owner; bh=6v6VHFXFCiRe9eoNj2FLlBwBnWgaCndKTTPL2fJFwhc=; b=fBoMVl97KRNGF2 jwl/hgY9mQ54V1hIyqgFWuxH7c3eUwtdlCzqpLFgSrlqM9HYiWnYeZ/MJofhMX1Y7VRCGwJKIsxbu qmUBmCSj3mlfWwwB9GnG1sEbqfUqDFAurHvx8oSAdjus1qzDF9JlmO39B2KX7LOC8BINyKIcZL/Q2 Ds+E6yGLxI/0x6dwnkcg1W89P//FzxLiTA2W+XxDiHwxeV8PYhiwWsJUdSRd//rLSArMGfIAvhQy6 kqNSo1zDvK+fOuFQlDdceEZ0hau9xtN8mqzIFf1yXE27YuqY8px2FWYWgsAB7AJsJ4bg8N/KCUKtX 5Oi+PYoIo/pjsSqsUEdg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gtuRz-0006qm-TP; Wed, 13 Feb 2019 13:19:43 +0000 Received: from outbound-smtp12.blacknight.com ([46.22.139.17]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gtuRm-0006ba-V4 for linux-arm-kernel@lists.infradead.org; Wed, 13 Feb 2019 13:19:33 +0000 Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp12.blacknight.com (Postfix) with ESMTPS id B28FF1C23FD for ; Wed, 13 Feb 2019 13:19:25 +0000 (GMT) Received: (qmail 25019 invoked from network); 13 Feb 2019 13:19:25 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[37.228.225.79]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 13 Feb 2019 13:19:25 -0000 Date: Wed, 13 Feb 2019 13:19:23 +0000 From: Mel Gorman To: Andrew Morton Subject: [PATCH] mm, page_alloc: Fix a division by zero error when boosting watermarks Message-ID: <20190213131923.GQ9565@techsingularity.net> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190213_051931_147166_98A3C94A X-CRM114-Status: GOOD ( 10.86 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andrea Arcangeli , Yury Norov , Catalin Marinas , Will Deacon , linux-kernel@vger.kernel.org, Michal Hocko , linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, David Rientjes , Vlastimil Babka Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP 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 either very early in boot or if the high watermark is very small. This patch checks for the conditions and avoids boosting in those cases. Fixes: 1c30844d2dfe ("mm: reclaim small amounts of memory when an external fragmentation event occurs") Reported-and-tested-by: Yury Norov Signed-off-by: Mel Gorman Tested-by: Will Deacon --- mm/page_alloc.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d295c9bc01a8..ae7e4ba5b9f5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2170,6 +2170,11 @@ static inline void boost_watermark(struct zone *zone) max_boost = mult_frac(zone->_watermark[WMARK_HIGH], watermark_boost_factor, 10000); + + /* high watermark be be uninitialised or very small */ + if (!max_boost) + return; + max_boost = max(pageblock_nr_pages, max_boost); zone->watermark_boost = min(zone->watermark_boost + pageblock_nr_pages,