From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga06.intel.com (mga06.intel.com [134.134.136.31]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 12C7421A09130 for ; Wed, 10 Oct 2018 08:28:04 -0700 (PDT) Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap 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> From: Alexander Duyck Message-ID: Date: Wed, 10 Oct 2018 08:27:58 -0700 MIME-Version: 1.0 In-Reply-To: <20181010125211.GA45572@tiger-server> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Dan Williams , Pasha Tatashin , Michal Hocko , linux-nvdimm , Dave Hansen , Linux Kernel Mailing List , Linux MM , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , rppt@linux.vnet.ibm.com, Andrew Morton , Ingo Molnar , "Kirill A. Shutemov" List-ID: 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. >> >> 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