From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx188.postini.com [74.125.245.188]) by kanga.kvack.org (Postfix) with SMTP id 8476E6B0007 for ; Thu, 31 Jan 2013 04:44:58 -0500 (EST) Message-ID: <510A3CE6.202@cn.fujitsu.com> Date: Thu, 31 Jan 2013 17:44:06 +0800 From: Tang Chen 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> In-Reply-To: <1359622123.1391.19.camel@kernel> Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8; format=flowed Sender: owner-linux-mm@kvack.org List-ID: To: Simon Jeons Cc: 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, wujianguo@huawei.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 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. >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. 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