From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f199.google.com (mail-pf1-f199.google.com [209.85.210.199]) by kanga.kvack.org (Postfix) with ESMTP id 1651D6B0006 for ; Wed, 10 Oct 2018 21:39:14 -0400 (EDT) Received: by mail-pf1-f199.google.com with SMTP id g72-v6so6551525pfk.9 for ; Wed, 10 Oct 2018 18:39:14 -0700 (PDT) Received: from mga14.intel.com (mga14.intel.com. [192.55.52.115]) by mx.google.com with ESMTPS id v14-v6si25607777plo.208.2018.10.10.18.39.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Oct 2018 18:39:12 -0700 (PDT) Date: Thu, 11 Oct 2018 16:17:54 +0800 From: Yi Zhang Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Message-ID: <20181011081754.GA51021@tiger-server> References: <20180925200551.3576.18755.stgit@localhost.localdomain> <20180925202053.3576.66039.stgit@localhost.localdomain> <20181009170051.GA40606@tiger-server> <25092df0-b7b4-d456-8409-9c004cb6e422@linux.intel.com> <20181010125211.GA45572@tiger-server> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Alexander Duyck Cc: Dan Williams , Pasha Tatashin , Michal Hocko , linux-nvdimm , Dave Hansen , Linux Kernel Mailing List , Linux MM , =?utf-8?B?SsOpcsO0bWU=?= Glisse , rppt@linux.vnet.ibm.com, Andrew Morton , Ingo Molnar , "Kirill A. Shutemov" On 2018-10-10 at 08:27:58 -0700, Alexander Duyck wrote: > > > On 10/10/2018 5:52 AM, Yi Zhang wrote: > >On 2018-10-09 at 14:19:32 -0700, Dan Williams wrote: > >>On Tue, Oct 9, 2018 at 1:34 PM Alexander Duyck > >> wrote: > >>> > >>>On 10/9/2018 11:04 AM, Dan Williams wrote: > >>>>On Tue, Oct 9, 2018 at 3:21 AM Yi Zhang wrote: > >>[..] > >>>>That comment is incorrect, device-pages are never onlined. So I think > >>>>we can just skip that call to __SetPageReserved() unless the memory > >>>>range is MEMORY_DEVICE_{PRIVATE,PUBLIC}. > >>>> > >>> > >>>When pages are "onlined" via __free_pages_boot_core they clear the > >>>reserved bit, that is the reason for the comment. The reserved bit is > >>>meant to indicate that the page cannot be swapped out or moved based on > >>>the description of the bit. > >> > >>...but ZONE_DEVICE pages are never onlined so I would expect > >>memmap_init_zone_device() to know that detail. > >> > >>>I would think with that being the case we still probably need the call > >>>to __SetPageReserved to set the bit with the expectation that it will > >>>not be cleared for device-pages since the pages are not onlined. > >>>Removing the call to __SetPageReserved would probably introduce a number > >>>of regressions as there are multiple spots that use the reserved bit to > >>>determine if a page can be swapped out to disk, mapped as system memory, > >>>or migrated. > > > >Another things, it seems page_init/set_reserved already been done in the > >move_pfn_range_to_zone > > |-->memmap_init_zone > > |-->for_each_page_in_pfn > > |-->__init_single_page > > |-->SetPageReserved > > > >Why we haven't remove these redundant initial in memmap_init_zone? > > > >Correct me if I missed something. > > In this case it isn't redundant as only the vmmemmap pages are initialized > in memmap_init_zone now. So all of the pages that are going to be used as > device pages are not initialized until the call to memmap_init_zone_device. > What I did is split the initialization of the pages into two parts in order > to allow us to initialize the pages outside of the hotplug lock. Ah.. I saw that, Thanks the explanation, so that is we only need to care about the device pages reserved flag, and plan to remove that. > > >> > >>Right, this is what Yi is working on... the PageReserved flag is > >>problematic for KVM. Auditing those locations it seems as long as we > >>teach hibernation to avoid ZONE_DEVICE ranges we can safely not set > >>the reserved flag for DAX pages. What I'm trying to avoid is a local > >>KVM hack to check for DAX pages when the Reserved flag is not > >>otherwise needed. > >Thanks Dan. Provide the patch link. > > > >https://lore.kernel.org/lkml/cover.1536342881.git.yi.z.zhang@linux.intel.com > > So it looks like your current logic is just working around the bit then > since it just allows for reserved DAX pages. > > > _______________________________________________ > Linux-nvdimm mailing list > Linux-nvdimm@lists.01.org > https://lists.01.org/mailman/listinfo/linux-nvdimm