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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 A06F7C4CEC9 for ; Wed, 18 Sep 2019 02:43:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7CE3F21897 for ; Wed, 18 Sep 2019 02:43:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726804AbfIRCnz convert rfc822-to-8bit (ORCPT ); Tue, 17 Sep 2019 22:43:55 -0400 Received: from tyo161.gate.nec.co.jp ([114.179.232.161]:57287 "EHLO tyo161.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725865AbfIRCnz (ORCPT ); Tue, 17 Sep 2019 22:43:55 -0400 Received: from mailgate01.nec.co.jp ([114.179.233.122]) by tyo161.gate.nec.co.jp (8.15.1/8.15.1) with ESMTPS id x8I2hZUN003725 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 18 Sep 2019 11:43:35 +0900 Received: from mailsv01.nec.co.jp (mailgate-v.nec.co.jp [10.204.236.94]) by mailgate01.nec.co.jp (8.15.1/8.15.1) with ESMTP id x8I2hZOM024135; Wed, 18 Sep 2019 11:43:35 +0900 Received: from mail01b.kamome.nec.co.jp (mail01b.kamome.nec.co.jp [10.25.43.2]) by mailsv01.nec.co.jp (8.15.1/8.15.1) with ESMTP id x8I2h1PV029819; Wed, 18 Sep 2019 11:43:35 +0900 Received: from bpxc99gp.gisp.nec.co.jp ([10.38.151.152] [10.38.151.152]) by mail02.kamome.nec.co.jp with ESMTP id BT-MMP-8629292; Wed, 18 Sep 2019 11:28:45 +0900 Received: from BPXM20GP.gisp.nec.co.jp ([10.38.151.212]) by BPXC24GP.gisp.nec.co.jp ([10.38.151.152]) with mapi id 14.03.0439.000; Wed, 18 Sep 2019 11:28:44 +0900 From: Toshiki Fukasawa To: Waiman Long , Qian Cai , David Hildenbrand , "linux-mm@kvack.org" , "dan.j.williams@intel.com" CC: Toshiki Fukasawa , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "mhocko@kernel.org" , "adobriyan@gmail.com" , "hch@lst.de" , "sfr@canb.auug.org.au" , "mst@redhat.com" , Naoya Horiguchi , Junichi Nomura Subject: Re: [RFC PATCH v2] mm: initialize struct pages reserved by ZONE_DEVICE driver. Thread-Topic: [RFC PATCH v2] mm: initialize struct pages reserved by ZONE_DEVICE driver. Thread-Index: AQHVZIp2xk1cU6nEkk+ez7kL5reVFKcdvuyAgAAVnwCAAAk8gIAEZuMAgAAgogCADDvdgIAATZsAgACQNwCAAAkNAIAAC/EAgACd24A= Date: Wed, 18 Sep 2019 02:28:44 +0000 Message-ID: References: <20190906081027.15477-1-t-fukasawa@vx.jp.nec.com> <40a1ce2e-1384-b869-97d0-7195b5b47de0@redhat.com> <6a99e003-e1ab-b9e8-7b25-bc5605ab0eb2@vx.jp.nec.com> <31fd3c86-5852-1863-93bd-8df9da9f95b4@vx.jp.nec.com> <38e58d23-c20b-4e68-5f56-20bba2be2d6c@redhat.com> <59c946f8-843d-c017-f342-d007a5e14a85@redhat.com> <1568737304.5576.162.camel@lca.pw> In-Reply-To: Accept-Language: ja-JP, en-US Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.34.125.135] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: <89A9A5B4A12A6343BA851F1A768C718D@gisp.nec.co.jp> Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-TM-AS-MML: disable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/09/18 2:04, Waiman Long wrote: > On 9/17/19 12:21 PM, Qian Cai wrote: >> On Tue, 2019-09-17 at 11:49 -0400, Waiman Long wrote: >>> On 9/17/19 3:13 AM, David Hildenbrand wrote: >>>> On 17.09.19 04:34, Toshiki Fukasawa wrote: >>>>> On 2019/09/09 16:46, David Hildenbrand wrote: >>>>>> Let's take a step back here to understand the issues I am aware of. I >>>>>> think we should solve this for good now: >>>>>> >>>>>> A PFN walker takes a look at a random PFN at a random point in time. It >>>>>> finds a PFN with SECTION_MARKED_PRESENT && !SECTION_IS_ONLINE. The >>>>>> options are: >>>>>> >>>>>> 1. It is buddy memory (add_memory()) that has not been online yet. The >>>>>> memmap contains garbage. Don't access. >>>>>> >>>>>> 2. It is ZONE_DEVICE memory with a valid memmap. Access it. >>>>>> >>>>>> 3. It is ZONE_DEVICE memory with an invalid memmap, because the section >>>>>> is only partially present: E.g., device starts at offset 64MB within a >>>>>> section or the device ends at offset 64MB within a section. Don't access it. >>>>> I don't agree with case #3. In the case, struct page area is not allocated on >>>>> ZONE_DEVICE, but is allocated on system memory. So I think we can access the >>>>> struct pages. What do you mean "invalid memmap"? >>>> No, that's not the case. There is no memory, especially not system >>>> memory. We only allow partially present sections (sub-section memory >>>> hotplug) for ZONE_DEVICE. >>>> >>>> invalid memmap == memmap was not initialized == struct pages contains >>>> garbage. There is a memmap, but accessing it (e.g., pfn_to_nid()) will >>>> trigger a BUG. >>>> >>> As long as the page structures exist, they should be initialized to some >>> known state. We could set PagePoison for those invalid memmap. It is the >> Sounds like you want to run page_init_poison() by default. > > Yes for those pages that are not initialized otherwise. I don't want to > run page_init_poison() for the whole ZONE_DEVICE memory range as it can > take a while if we are talking about TBs of persistent memory. Also most > of the pages will be reinitialized anyway in the init process. So it is > mostly a wasted effort. However, for those reserved pages that are not > being exported to the memory management layer, having them initialized > to a known state will cause less problem down the road. > The same can be said about altmap->reserve. I think it should be initialized since the struct page exists. Thanks, Toshiki Fukasawa