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[209.132.180.67]) by mx.google.com with ESMTP id 123-v6si1813613pfd.201.2018.09.27.04.09.38; Thu, 27 Sep 2018 04:09:53 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727356AbeI0R1O (ORCPT + 99 others); Thu, 27 Sep 2018 13:27:14 -0400 Received: from mx2.suse.de ([195.135.220.15]:59866 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726948AbeI0R1O (ORCPT ); Thu, 27 Sep 2018 13:27:14 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 28ADEADE4; Thu, 27 Sep 2018 11:09:28 +0000 (UTC) Date: Thu, 27 Sep 2018 13:09:26 +0200 From: Michal Hocko To: Alexander Duyck Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, pavel.tatashin@microsoft.com, dave.jiang@intel.com, dave.hansen@intel.com, jglisse@redhat.com, rppt@linux.vnet.ibm.com, dan.j.williams@intel.com, logang@deltatee.com, mingo@kernel.org, kirill.shutemov@linux.intel.com Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Message-ID: <20180927110926.GE6278@dhcp22.suse.cz> References: <20180925200551.3576.18755.stgit@localhost.localdomain> <20180925202053.3576.66039.stgit@localhost.localdomain> <20180926075540.GD6278@dhcp22.suse.cz> <6f87a5d7-05e2-00f4-8568-bb3521869cea@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6f87a5d7-05e2-00f4-8568-bb3521869cea@linux.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 26-09-18 11:25:37, Alexander Duyck wrote: > > > On 9/26/2018 12:55 AM, Michal Hocko wrote: > > On Tue 25-09-18 13:21:24, Alexander Duyck wrote: > > > The ZONE_DEVICE pages were being initialized in two locations. One was with > > > the memory_hotplug lock held and another was outside of that lock. The > > > problem with this is that it was nearly doubling the memory initialization > > > time. Instead of doing this twice, once while holding a global lock and > > > once without, I am opting to defer the initialization to the one outside of > > > the lock. This allows us to avoid serializing the overhead for memory init > > > and we can instead focus on per-node init times. > > > > > > One issue I encountered is that devm_memremap_pages and > > > hmm_devmmem_pages_create were initializing only the pgmap field the same > > > way. One wasn't initializing hmm_data, and the other was initializing it to > > > a poison value. Since this is something that is exposed to the driver in > > > the case of hmm I am opting for a third option and just initializing > > > hmm_data to 0 since this is going to be exposed to unknown third party > > > drivers. > > > > Why cannot you pull move_pfn_range_to_zone out of the hotplug lock? In > > other words why are you making zone device even more special in the > > generic hotplug code when it already has its own means to initialize the > > pfn range by calling move_pfn_range_to_zone. Not to mention the code > > duplication. > > So there were a few things I wasn't sure we could pull outside of the > hotplug lock. One specific example is the bits related to resizing the pgdat > and zone. I wanted to avoid pulling those bits outside of the hotplug lock. Why would that be a problem. There are dedicated locks for resizing. > The other bit that I left inside the hot-plug lock with this approach was > the initialization of the pages that contain the vmemmap. Again, why this is needed? > > That being said I really dislike this patch. > > In my mind this was a patch that "killed two birds with one stone". I had > two issues to address, the first one being the fact that we were performing > the memmap_init_zone while holding the hotplug lock, and the other being the > loop that was going through and initializing pgmap in the hmm and memremap > calls essentially added another 20 seconds (measured for 3TB of memory per > node) to the init time. With this patch I was able to cut my init time per > node by that 20 seconds, and then made it so that we could scale as we added > nodes as they could run in parallel. > > With that said I am open to suggestions if you still feel like I need to > follow this up with some additional work. I just want to avoid introducing > any regressions in regards to functionality or performance. Yes, I really do prefer this to be done properly rather than tweak it around because of uncertainties. -- Michal Hocko SUSE Labs