From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f48.google.com (mail-pa0-f48.google.com [209.85.220.48]) by kanga.kvack.org (Postfix) with ESMTP id E63636B0253 for ; Mon, 11 Apr 2016 06:40:18 -0400 (EDT) Received: by mail-pa0-f48.google.com with SMTP id zm5so119490969pac.0 for ; Mon, 11 Apr 2016 03:40:18 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id b90si2858241pfd.128.2016.04.11.03.40.18 for ; Mon, 11 Apr 2016 03:40:18 -0700 (PDT) Date: Mon, 11 Apr 2016 11:40:13 +0100 From: Will Deacon Subject: Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Message-ID: <20160411104013.GG15729@arm.com> References: <1459844572-53069-1-git-send-email-puck.chen@hisilicon.com> <20160407142148.GI5657@arm.com> <570B10B2.2000000@hisilicon.com> <570B5875.20804@hisilicon.com> <570B758E.7070005@hisilicon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Ard Biesheuvel Cc: Chen Feng , Mark Rutland , mhocko@suse.com, Laura Abbott , Dan Zhao , Yiping Xu , puck.chen@foxmail.com, albert.lubing@hisilicon.com, Catalin Marinas , suzhuangluan@hisilicon.com, "linux-kernel@vger.kernel.org" , linuxarm@huawei.com, "linux-mm@kvack.org" , kirill.shutemov@linux.intel.com, David Rientjes , oliver.fu@hisilicon.com, Andrew Morton , robin.murphy@arm.com, "linux-arm-kernel@lists.infradead.org" , saberlily.xia@hisilicon.com On Mon, Apr 11, 2016 at 12:31:53PM +0200, Ard Biesheuvel wrote: > On 11 April 2016 at 11:59, Chen Feng wrote: > > Please see the pg-tables below. > > > > > > With sparse and vmemmap enable. > > > > ---[ vmemmap start ]--- > > 0xffffffbdc0200000-0xffffffbdc4800000 70M RW NX SHD AF UXN MEM/NORMAL > > ---[ vmemmap end ]--- > > > > OK, I see what you mean now. Sorry for taking so long to catch up. > > > The board is 4GB, and the memap is 70MB > > 1G memory --- 14MB mem_map array. > > No, this is incorrect. 1 GB corresponds with 16 MB worth of struct > pages assuming sizeof(struct page) == 64 > > So you are losing 6 MB to rounding here, which I agree is significant. > I wonder if it makes sense to use a lower value for SECTION_SIZE_BITS > on 4k pages kernels, but perhaps we're better off asking the opinion > of the other cc'ees. You need to be really careful making SECTION_SIZE_BITS smaller because it has a direct correlation on the use of page->flags and you can end up running out of bits fairly easily. Will -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org