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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 73C2FC433B4 for ; Mon, 19 Apr 2021 03:45:29 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E69F66100C for ; Mon, 19 Apr 2021 03:45:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E69F66100C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4FNt4l3RCFz3btb for ; Mon, 19 Apr 2021 13:45:27 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=arm.com (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=anshuman.khandual@arm.com; receiver=) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lists.ozlabs.org (Postfix) with ESMTP id 4FNt4M27Zcz2yx9 for ; Mon, 19 Apr 2021 13:45:05 +1000 (AEST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 97FD931B; Sun, 18 Apr 2021 20:45:01 -0700 (PDT) Received: from [10.163.74.113] (unknown [10.163.74.113]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1C1883F800; Sun, 18 Apr 2021 20:44:57 -0700 (PDT) Subject: Re: [PATCH V2] mm/page_alloc: Ensure that HUGETLB_PAGE_ORDER is less than MAX_ORDER To: David Hildenbrand , linux-mm@kvack.org, akpm@linux-foundation.org References: <1618199302-29335-1-git-send-email-anshuman.khandual@arm.com> <09284b9a-cfe1-fc49-e1f6-3cf0c1b74c76@arm.com> <162877dd-e6ba-d465-d301-2956bb034429@redhat.com> From: Anshuman Khandual Message-ID: Date: Mon, 19 Apr 2021 09:15:49 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <162877dd-e6ba-d465-d301-2956bb034429@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-ia64@vger.kernel.org" , "linuxppc-dev @ lists . ozlabs . org" , linux-kernel@vger.kernel.org, Michal Hocko , Christoph Lameter , Mel Gorman , Vlastimil Babka Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 4/12/21 2:17 PM, David Hildenbrand wrote: > On 12.04.21 10:06, Anshuman Khandual wrote: >> + linuxppc-dev@lists.ozlabs.org >> + linux-ia64@vger.kernel.org >> >> On 4/12/21 9:18 AM, Anshuman Khandual wrote: >>> pageblock_order must always be less than MAX_ORDER, otherwise it might lead >>> to an warning during boot. A similar problem got fixed on arm64 platform >>> with the commit 79cc2ed5a716 ("arm64/mm: Drop THP conditionality from >>> FORCE_MAX_ZONEORDER"). Assert the above condition before HUGETLB_PAGE_ORDER >>> gets assigned as pageblock_order. This will help detect the problem earlier >>> on platforms where HUGETLB_PAGE_SIZE_VARIABLE is enabled. >>> >>> Cc: David Hildenbrand >>> Cc: Andrew Morton >>> Cc: linux-mm@kvack.org >>> Cc: linux-kernel@vger.kernel.org >>> Signed-off-by: Anshuman Khandual >>> --- >>> Changes in V2: >>> >>> - Changed WARN_ON() to BUILD_BUG_ON() per David >>> >>> Changes in V1: >>> >>> https://patchwork.kernel.org/project/linux-mm/patch/1617947717-2424-1-git-send-email-anshuman.khandual@arm.com/ >>> >>> mm/page_alloc.c | 11 +++++++++-- >>> 1 file changed, 9 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index cfc72873961d..19283bff4bec 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -6875,10 +6875,17 @@ void __init set_pageblock_order(void) >>> if (pageblock_order) >>> return; >>> - if (HPAGE_SHIFT > PAGE_SHIFT) >>> + if (HPAGE_SHIFT > PAGE_SHIFT) { >>> + /* >>> + * pageblock_order must always be less than >>> + * MAX_ORDER. So does HUGETLB_PAGE_ORDER if >>> + * that is being assigned here. >>> + */ >>> + BUILD_BUG_ON(HUGETLB_PAGE_ORDER >= MAX_ORDER); >> >> Unfortunately the build test fails on both the platforms (powerpc and ia64) >> which subscribe HUGETLB_PAGE_SIZE_VARIABLE and where this check would make >> sense. I some how overlooked the cross compile build failure that actually >> detected this problem. >> >> But wondering why this assert is not holding true ? and how these platforms >> do not see the warning during boot (or do they ?) at mm/vmscan.c:1092 like >> arm64 did. >> >> static int __fragmentation_index(unsigned int order, struct contig_page_info *info) >> { >> unsigned long requested = 1UL << order; >> >> if (WARN_ON_ONCE(order >= MAX_ORDER)) >> return 0; >> .... >> >> Can pageblock_order really exceed MAX_ORDER - 1 ? > > Ehm, for now I was under the impression that such configurations wouldn't exist. > > And originally, HUGETLB_PAGE_SIZE_VARIABLE was introduced to handle hugepage sizes that all *smaller* than MAX_ORDER - 1: See d9c234005227 ("Do not depend on MAX_ORDER when grouping pages by mobility") Right. > > > However, looking into init_cma_reserved_pageblock(): > > if (pageblock_order >= MAX_ORDER) { > i = pageblock_nr_pages; > ... > } > > > But it's kind of weird, isn't it? Let's assume we have MAX_ORDER - 1 correspond to 4 MiB and pageblock_order correspond to 8 MiB. > > Sure, we'd be grouping pages in 8 MiB chunks, however, we cannot even allocate 8 MiB chunks via the buddy. So only alloc_contig_range() could really grab them (IOW: gigantic pages). Right. > > Further, we have code like deferred_free_range(), where we end up calling __free_pages_core()->...->__free_one_page() with pageblock_order. Wouldn't we end up setting the buddy order to something > MAX_ORDER -1 on that path? Agreed. > > Having pageblock_order > MAX_ORDER feels wrong and looks shaky. > Agreed, definitely does not look right. Lets see what other folks might have to say on this. + Christoph Lameter