From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D8945C4321A for ; Thu, 25 Apr 2019 15:25:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 02CE3206C0 for ; Thu, 25 Apr 2019 15:25:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556205956; bh=59I6dUdmKaNfnmPOyLiLVrGc1J4bM8FMIFPvAl3lNvc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=qd9/ELNnoGDw1AD92eYe67wu8FpScyMA6nAtuhs7iDOJNCqkFE5VVxNKXNK9YeaVp N73UXhO5/dK/2TEB97SaoHbheVPx20xZOXL4Qnq8ormsQdCDnca0G2znq5L5j9oNMo Lh7TPU4JUOKgDxvWC969WdDRmuC7IlWKuDqSW97E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728847AbfDYPZy (ORCPT ); Thu, 25 Apr 2019 11:25:54 -0400 Received: from mx2.suse.de ([195.135.220.15]:41694 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727337AbfDYPZy (ORCPT ); Thu, 25 Apr 2019 11:25:54 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 6F7B5AF26; Thu, 25 Apr 2019 15:25:52 +0000 (UTC) Date: Thu, 25 Apr 2019 17:25:50 +0200 From: Michal Hocko To: Pavel Tatashin Cc: jmorris@namei.org, sashal@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, akpm@linux-foundation.org, dave.hansen@linux.intel.com, dan.j.williams@intel.com, keith.busch@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, zwisler@kernel.org, thomas.lendacky@amd.com, ying.huang@intel.com, fengguang.wu@intel.com, bp@suse.de, bhelgaas@google.com, baiyaowei@cmss.chinamobile.com, tiwai@suse.de, jglisse@redhat.com, catalin.marinas@arm.com, will.deacon@arm.com, rppt@linux.vnet.ibm.com, ard.biesheuvel@linaro.org, andrew.murray@arm.com, james.morse@arm.com, marc.zyngier@arm.com, sboyd@kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] arm64: configurable sparsemem section size Message-ID: <20190425152550.GY12751@dhcp22.suse.cz> References: <20190423203843.2898-1-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190423203843.2898-1-pasha.tatashin@soleen.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 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? -- Michal Hocko SUSE Labs