From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) (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 10D1E2115990A for ; Thu, 27 Sep 2018 04:09:29 -0700 (PDT) Date: Thu, 27 Sep 2018 13:09:26 +0200 From: Michal Hocko 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-Disposition: inline In-Reply-To: <6f87a5d7-05e2-00f4-8568-bb3521869cea@linux.intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Alexander Duyck Cc: pavel.tatashin@microsoft.com, linux-nvdimm@lists.01.org, dave.hansen@intel.com, linux-kernel@vger.kernel.org, mingo@kernel.org, linux-mm@kvack.org, jglisse@redhat.com, rppt@linux.vnet.ibm.com, akpm@linux-foundation.org, kirill.shutemov@linux.intel.com List-ID: 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 _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm