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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 40190C433DB for ; Mon, 15 Feb 2021 21:24:55 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B574E64DFF for ; Mon, 15 Feb 2021 21:24:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B574E64DFF Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 19AD28D0144; Mon, 15 Feb 2021 16:24:54 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 130128D0140; Mon, 15 Feb 2021 16:24:54 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 016DE8D0144; Mon, 15 Feb 2021 16:24:53 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0030.hostedemail.com [216.40.44.30]) by kanga.kvack.org (Postfix) with ESMTP id DA2DA8D0140 for ; Mon, 15 Feb 2021 16:24:53 -0500 (EST) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id A9F32182CFFA2 for ; Mon, 15 Feb 2021 21:24:53 +0000 (UTC) X-FDA: 77821782066.09.nut83_1013a9e2763e Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin09.hostedemail.com (Postfix) with ESMTP id 93038181D2077 for ; Mon, 15 Feb 2021 21:24:53 +0000 (UTC) X-HE-Tag: nut83_1013a9e2763e X-Filterd-Recvd-Size: 3979 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Mon, 15 Feb 2021 21:24:53 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 7930B64DF0; Mon, 15 Feb 2021 21:24:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1613424292; bh=NP7OZUIQV/dje06OdQt5TFb4vM8T/LsPqUZ2gqmBI/4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mLNfURDgfVU5V4mSwtJ4K4GTVBCSN8MHS69bE0Yu8ALlAHrDMn9VADZXn2hwGMsXi m/1Fko5D9P5r3vA12HEOSGdA6/tnfiwrWGrhmLhzt4nDTpgIFRBiOtt6G4kxwK39N3 kxqeq+iUoqBCG78EcF9n72X4E3FqbnMBC3qMYSxMBXqFCA9URMxzLOA3hn4BAV3CUb Rcns3zFZJSzB4sF2RJKQWEUejb10BJrzL2Ru07ZLHjza8iykuFMgx6/at9cSxQhEpE dziA8uWuD/ibQKF3QxlALWP//zGeFQkIB4t5ho4upuPDEEKfm3PBOxdBIOYuNGSyIR QXTWUd06bnzMg== Date: Mon, 15 Feb 2021 23:24:40 +0200 From: Mike Rapoport To: Michal Hocko Cc: Mel Gorman , David Hildenbrand , Andrew Morton , Andrea Arcangeli , Baoquan He , Borislav Petkov , Chris Wilson , "H. Peter Anvin" , Ingo Molnar , Linus Torvalds , =?utf-8?Q?=C5=81ukasz?= Majczak , Mike Rapoport , Qian Cai , "Sarvela, Tomi P" , Thomas Gleixner , Vlastimil Babka , linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH v5 1/1] mm: refactor initialization of struct page for holes in memory layout Message-ID: <20210215212440.GA1307762@kernel.org> References: <20210208110820.6269-1-rppt@kernel.org> <20210214180016.GO242749@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Mon, Feb 15, 2021 at 10:00:31AM +0100, Michal Hocko wrote: > On Sun 14-02-21 20:00:16, Mike Rapoport wrote: > > On Fri, Feb 12, 2021 at 02:18:20PM +0100, Michal Hocko wrote: > > > We can correctly set the zone links for the reserved pages for holes in the > > middle of a zone based on the architecture constraints and with only the > > holes in the beginning/end of the memory will be not spanned by any > > node/zone which in practice does not seem to be a problem as the VM_BUG_ON > > in set_pfnblock_flags_mask() never triggered on pfn 0. > > I really fail to see what you mean by correct zone/node for a memory > range which is not associated with any real node. We know architectural zone constraints, so we can have always have 1:1 match from pfn to zone. Node indeed will be a guess. > > > I am sorry, I haven't followed previous discussions. Has the removal of > > > the VM_BUG_ON been considered as an immediate workaround? > > > > It was never discussed, but I'm not sure it's a good idea. > > > > Judging by the commit message that introduced the VM_BUG_ON (commit > > 86051ca5eaf5 ("mm: fix usemap initialization")) there was yet another > > inconsistency in the memory map that required a special care. > > Can we actually explore that path before adding yet additional > complexity and potentially a very involved fix for a subtle problem? This patch was intended as a fix for inconsistency of the memory map that is the root cause for triggering this VM_BUG_ON and other corner case problems. The previous version [1] is less involved as it does not extend node/zone spans. [1] https://lore.kernel.org/lkml/20210130221035.4169-3-rppt@kernel.org -- Sincerely yours, Mike.