From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx156.postini.com [74.125.245.156]) by kanga.kvack.org (Postfix) with SMTP id A31466B0008 for ; Thu, 31 Jan 2013 20:58:42 -0500 (EST) Message-ID: <510B20F2.20906@huawei.com> Date: Fri, 1 Feb 2013 09:57:06 +0800 From: Jianguo Wu MIME-Version: 1.0 Subject: Re: [PATCH v6 00/15] memory-hotplug: hot-remove physical memory References: <1357723959-5416-1-git-send-email-tangchen@cn.fujitsu.com> <1359463973.1624.15.camel@kernel> <5108F2B3.3090506@cn.fujitsu.com> <1359595344.1557.13.camel@kernel> <5109E59F.5080104@cn.fujitsu.com> <1359613162.1587.0.camel@kernel> <510A18FA.2010107@cn.fujitsu.com> <1359622123.1391.19.camel@kernel> <510A3CE6.202@cn.fujitsu.com> <1359628705.2048.5.camel@kernel> <510B1B4B.5080207@huawei.com> <1359682576.3574.1.camel@kernel> In-Reply-To: <1359682576.3574.1.camel@kernel> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Simon Jeons Cc: Tang Chen , akpm@linux-foundation.org, rientjes@google.com, len.brown@intel.com, benh@kernel.crashing.org, paulus@samba.org, cl@linux.com, minchan.kim@gmail.com, kosaki.motohiro@jp.fujitsu.com, isimatu.yasuaki@jp.fujitsu.com, wency@cn.fujitsu.com, hpa@zytor.com, linfeng@cn.fujitsu.com, laijs@cn.fujitsu.com, mgorman@suse.de, yinghai@kernel.org, glommer@parallels.com, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-acpi@vger.kernel.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-ia64@vger.kernel.org, cmetcalf@tilera.com, sparclinux@vger.kernel.org On 2013/2/1 9:36, Simon Jeons wrote: > On Fri, 2013-02-01 at 09:32 +0800, Jianguo Wu wrote: >> On 2013/1/31 18:38, Simon Jeons wrote: >> >>> Hi Tang, >>> On Thu, 2013-01-31 at 17:44 +0800, Tang Chen wrote: >>>> Hi Simon, >>>> >>>> On 01/31/2013 04:48 PM, Simon Jeons wrote: >>>>> Hi Tang, >>>>> On Thu, 2013-01-31 at 15:10 +0800, Tang Chen wrote: >>>>> >>>>> 1. IIUC, there is a button on machine which supports hot-remove memory, >>>>> then what's the difference between press button and echo to /sys? >>>> >>>> No important difference, I think. Since I don't have the machine you are >>>> saying, I cannot surely answer you. :) >>>> AFAIK, pressing the button means trigger the hotplug from hardware, sysfs >>>> is just another entrance. At last, they will run into the same code. >>>> >>>>> 2. Since kernel memory is linear mapping(I mean direct mapping part), >>>>> why can't put kernel direct mapping memory into one memory device, and >>>>> other memory into the other devices? >>>> >>>> We cannot do that because in that way, we will lose NUMA performance. >>>> >>>> If you know NUMA, you will understand the following example: >>>> >>>> node0: node1: >>>> cpu0~cpu15 cpu16~cpu31 >>>> memory0~memory511 memory512~memory1023 >>>> >>>> cpu16~cpu31 access memory16~memory1023 much faster than memory0~memory511. >>>> If we set direct mapping area in node0, and movable area in node1, then >>>> the kernel code running on cpu16~cpu31 will have to access >>>> memory0~memory511. >>>> This is a terrible performance down. >>> >>> So if config NUMA, kernel memory will not be linear mapping anymore? For >>> example, >>> >>> Node 0 Node 1 >>> >>> 0 ~ 10G 11G~14G >>> >>> kernel memory only at Node 0? Can part of kernel memory also at Node 1? >>> >>> How big is kernel direct mapping memory in x86_64? Is there max limit? >> >> >> Max kernel direct mapping memory in x86_64 is 64TB. > > For example, I have 8G memory, all of them will be direct mapping for > kernel? then userspace memory allocated from where? Direct mapping memory means you can use __va() and pa(), but not means that them can be only used by kernel, them can be used by user-space too, as long as them are free. > >> >>> It seems that only around 896MB on x86_32. >>> >>>> >>>>> As you know x86_64 don't need >>>>> highmem, IIUC, all kernel memory will linear mapping in this case. Is my >>>>> idea available? If is correct, x86_32 can't implement in the same way >>>>> since highmem(kmap/kmap_atomic/vmalloc) can map any address, so it's >>>>> hard to focus kernel memory on single memory device. >>>> >>>> Sorry, I'm not quite familiar with x86_32 box. >>>> >>>>> 3. In current implementation, if memory hotplug just need memory >>>>> subsystem and ACPI codes support? Or also needs firmware take part in? >>>>> Hope you can explain in details, thanks in advance. :) >>>> >>>> We need firmware take part in, such as SRAT in ACPI BIOS, or the firmware >>>> based memory migration mentioned by Liu Jiang. >>> >>> Is there any material about firmware based memory migration? >>> >>>> >>>> So far, I only know this. :) >>>> >>>>> 4. What's the status of memory hotplug? Apart from can't remove kernel >>>>> memory, other things are fully implementation? >>>> >>>> I think the main job is done for now. And there are still bugs to fix. >>>> And this functionality is not stable. >>>> >>>> Thanks. :) >>> >>> >>> -- >>> 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 >>> >>> . >>> >> >> >> > > > > . > -- 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