Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933984AbcDLOD6 (ORCPT ); Tue, 12 Apr 2016 10:03:58 -0400 Received: from mail-pf0-f196.google.com ([209.85.192.196]:35223 "EHLO mail-pf0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932221AbcDLODt convert rfc822-to-8bit (ORCPT ); Tue, 12 Apr 2016 10:03:49 -0400 Subject: Re: [PATCH 1/2] arm64: mem-model: add flatmem model for arm64 Mime-Version: 1.0 (Apple Message framework v1283) Content-Type: text/plain; charset=windows-1252 From: Jungseok Lee In-Reply-To: <570B10B2.2000000@hisilicon.com> Date: Tue, 12 Apr 2016 23:03:41 +0900 Cc: Will Deacon , mhocko@suse.com, Laura Abbott , Catalin Marinas , ard.biesheuvel@linaro.org, Mark Rutland , Andrew Morton , robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, "linux-kernel@vger.kernel.org List" , "Kirill A. Shutemov" , rientjes@google.com, linux-mm@kvack.org, puck.chen@foxmail.com, oliver.fu@hisilicon.com, linuxarm@huawei.com, dan.zhao@hisilicon.com, suzhuangluan@hisilicon.com, yudongbin@hislicon.com, albert.lubing@hisilicon.com, xuyiping@hisilicon.com, saberlily.xia@hisilicon.com Content-Transfer-Encoding: 8BIT Message-Id: References: <1459844572-53069-1-git-send-email-puck.chen@hisilicon.com> <20160407142148.GI5657@arm.com> <570B10B2.2000000@hisilicon.com> To: Chen Feng X-Mailer: Apple Mail (2.1283) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2807 Lines: 79 On Apr 11, 2016, at 11:49 AM, Chen Feng wrote: Dear Chen, > Hi will, > Thanks for review. > > On 2016/4/7 22:21, Will Deacon wrote: >> On Tue, Apr 05, 2016 at 04:22:51PM +0800, Chen Feng wrote: >>> We can reduce the memory allocated at mem-map >>> by flatmem. >>> >>> currently, the default memory-model in arm64 is >>> sparse memory. The mem-map array is not freed in >>> this scene. If the physical address is too long, >>> it will reserved too much memory for the mem-map >>> array. >> >> Can you elaborate a bit more on this, please? We use the vmemmap, so any >> spaces between memory banks only burns up virtual space. What exactly is >> the problem you're seeing that makes you want to use flatmem (which is >> probably unsuitable for the majority of arm64 machines). >> > The root cause we want to use flat-mem is the mam_map alloced in sparse-mem > is not freed. > > take a look at here: > arm64/mm/init.c > void __init mem_init(void) > { > #ifndef CONFIG_SPARSEMEM_VMEMMAP > free_unused_memmap(); > #endif > } > > Memory layout (3GB) > > 0 1.5G 2G 3.5G 4G > | | | | | > +--------------+------+---------------+--------------+ > | MEM | hole | MEM | IO (regs) | > +--------------+------+---------------+--------------+ > > > Memory layout (4GB) > > 0 3.5G 4G 4.5G > | | | | > +-------------------------------------+--------------+-------+ > | MEM | IO (regs) | MEM | > +-------------------------------------+--------------+-------+ > > Currently, the sparse memory section is 1GB. > > 3GB ddr: the 1.5 ~2G and 3.5 ~ 4G are holes. > 3GB ddr: the 3.5 ~ 4G and 4.5 ~ 5G are holes. > > This will alloc 1G/4K * (struct page) memory for mem_map array. > > We want to use flat-mem to reduce the alloced mem_map. > > I don't know why you tell us the flatmem is unsuitable for the > majority of arm64 machines. Can tell us the reason of it? > > And we are not going to limit the memdel in arm64, we just want to > make the flat-mem is an optional item in arm64. I've experienced the same problem and considered the ideas mentioned in this thread: flatmem and small SECTION_SIZE_BITS. However, I was reluctant to post any patch since the issue is highly related to memory map design document, [1], saying 1GB aligned RAM. The majority of arm64 platforms might follow the information although it is not spec. IOW, a machine I've played was at least unusual *at that time*, so I didn't consider upstream work. [1] http://infocenter.arm.com/help/topic/com.arm.doc.den0001c/DEN0001C_principles_of_arm_memory_maps.pdf Best Regards Jungseok Lee