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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 E9B0FC4CECD for ; Tue, 17 Sep 2019 17:04:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C44632067B for ; Tue, 17 Sep 2019 17:04:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730721AbfIQREh (ORCPT ); Tue, 17 Sep 2019 13:04:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38654 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730669AbfIQREh (ORCPT ); Tue, 17 Sep 2019 13:04:37 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 79063369D3; Tue, 17 Sep 2019 17:04:36 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-160.bos.redhat.com [10.18.17.160]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6C2F560126; Tue, 17 Sep 2019 17:04:29 +0000 (UTC) Subject: Re: [RFC PATCH v2] mm: initialize struct pages reserved by ZONE_DEVICE driver. To: Qian Cai , David Hildenbrand , Toshiki Fukasawa , "linux-mm@kvack.org" , "dan.j.williams@intel.com" Cc: "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 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> From: Waiman Long Organization: Red Hat Message-ID: Date: Tue, 17 Sep 2019 13:04:28 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <1568737304.5576.162.camel@lca.pw> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Tue, 17 Sep 2019 17:04:36 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Cheers, Longman