From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com (foss.arm.com [217.140.101.70]) by ml01.01.org (Postfix) with ESMTP id B622021217961 for ; Thu, 25 Apr 2019 08:31:46 -0700 (PDT) Date: Thu, 25 Apr 2019 16:31:38 +0100 From: Will Deacon Subject: Re: [PATCH] arm64: configurable sparsemem section size Message-ID: <20190425153138.GC25193@fuggles.cambridge.arm.com> References: <20190423203843.2898-1-pasha.tatashin@soleen.com> <20190425152550.GY12751@dhcp22.suse.cz> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190425152550.GY12751@dhcp22.suse.cz> 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: Michal Hocko Cc: tiwai@suse.de, catalin.marinas@arm.com, dave.hansen@linux.intel.com, linux-mm@kvack.org, baiyaowei@cmss.chinamobile.com, zwisler@kernel.org, sashal@kernel.org, linux-nvdimm@lists.01.org, jmorris@namei.org, ying.huang@intel.com, bp@suse.de, thomas.lendacky@amd.com, Pavel Tatashin , marc.zyngier@arm.com, jglisse@redhat.com, rppt@linux.vnet.ibm.com, bhelgaas@google.com, linux-arm-kernel@lists.infradead.org, ard.biesheuvel@linaro.org, sboyd@kernel.org, linux-kernel@vger.kernel.org, james.morse@arm.com, andrew.murray@arm.com, akpm@linux-foundation.org, fengguang.wu@intel.com List-ID: On Thu, Apr 25, 2019 at 05:25:50PM +0200, Michal Hocko wrote: > On Tue 23-04-19 16:38:43, Pavel Tatashin wrote: > > sparsemem section size determines the maximum size and alignment that > > is allowed to offline/online memory block. The bigger the size the less > > the clutter in /sys/devices/system/memory/*. On the other hand, however, > > there is less flexability in what granules of memory can be added and > > removed. > > > > Recently, it was enabled in Linux to hotadd persistent memory that > > can be either real NV device, or reserved from regular System RAM > > and has identity of devdax. > > > > The problem is that because ARM64's section size is 1G, and devdax must > > have 2M label section, the first 1G is always missed when device is > > attached, because it is not 1G aligned. > > > > Allow, better flexibility by making section size configurable. > > Is there any inherent reason (64k page size?) that enforces such a large > memsection? I gave *vague* memories of running out of bits in the page flags if we changed this, but that was a while back. If that's no longer the case, then I'm open to changing the value, but I really don't want to expose it as a Kconfig option as proposed in this patch. People won't have a clue what to set and it doesn't help at all with the single-Image effort. Will _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm