From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) (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 A599C21144CE3 for ; Wed, 10 Oct 2018 09:39:09 -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> <20181010095838.GG5873@dhcp22.suse.cz> From: Alexander Duyck Message-ID: Date: Wed, 10 Oct 2018 09:39:08 -0700 MIME-Version: 1.0 In-Reply-To: <20181010095838.GG5873@dhcp22.suse.cz> 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: Michal Hocko Cc: Pasha Tatashin , linux-nvdimm , Dave Hansen , Linux Kernel Mailing List , Ingo Molnar , Linux MM , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , rppt@linux.vnet.ibm.com, Andrew Morton , "Kirill A. Shutemov" List-ID: On 10/10/2018 2:58 AM, Michal Hocko wrote: > On Tue 09-10-18 13:26:41, Alexander Duyck wrote: > [...] >> 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. > > PageReserved is meant to tell any potential pfn walkers that might get > to this struct page to back off and not touch it. Even though > ZONE_DEVICE doesn't online pages in traditional sense it makes those > pages available for further use so the page reserved bit should be > cleared. So from what I can tell that isn't necessarily the case. Specifically if the pagemap type is MEMORY_DEVICE_PRIVATE or MEMORY_DEVICE_PUBLIC both are special cases where the memory may not be accessible to the CPU or cannot be pinned in order to allow for eviction. The specific case that Dan and Yi are referring to is for the type MEMORY_DEVICE_FS_DAX. For that type I could probably look at not setting the reserved bit. Part of me wants to say that we should wait and clear the bit later, but that would end up just adding time back to initialization. At this point I would consider the change more of a follow-up optimization rather than a fix though since this is tailoring things specifically for DAX versus the other ZONE_DEVICE types. _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm