From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx139.postini.com [74.125.245.139]) by kanga.kvack.org (Postfix) with SMTP id 255E16B0031 for ; Mon, 5 Aug 2013 09:39:52 -0400 (EDT) Message-ID: <51FFAAD1.9040405@cn.fujitsu.com> Date: Mon, 05 Aug 2013 21:38:25 +0800 From: Tang Chen MIME-Version: 1.0 Subject: Re: [PATCH v2 00/18] Arrange hotpluggable memory as ZONE_MOVABLE. References: <1375340800-19332-1-git-send-email-tangchen@cn.fujitsu.com> <51FFA393.2080301@zytor.com> In-Reply-To: <51FFA393.2080301@zytor.com> Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8; format=flowed Sender: owner-linux-mm@kvack.org List-ID: To: "H. Peter Anvin" Cc: rjw@sisk.pl, lenb@kernel.org, tglx@linutronix.de, mingo@elte.hu, akpm@linux-foundation.org, tj@kernel.org, trenn@suse.de, yinghai@kernel.org, jiang.liu@huawei.com, wency@cn.fujitsu.com, laijs@cn.fujitsu.com, isimatu.yasuaki@jp.fujitsu.com, izumi.taku@jp.fujitsu.com, mgorman@suse.de, minchan@kernel.org, mina86@mina86.com, gong.chen@linux.intel.com, vasilis.liaskovitis@profitbricks.com, lwoodman@redhat.com, riel@redhat.com, jweiner@redhat.com, prarit@redhat.com, zhangyanfei@cn.fujitsu.com, yanghy@cn.fujitsu.com, x86@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-acpi@vger.kernel.org Hi hpa, I'm sorry but I don't quite following it. On 08/05/2013 09:07 PM, H. Peter Anvin wrote: > On 08/01/2013 12:06 AM, Tang Chen wrote: >> This patch-set aims to solve some problems at system boot time >> to enhance memory hotplug functionality. >> >> [Background] >> >> The Linux kernel cannot migrate pages used by the kernel because >> of the kernel direct mapping. Since va = pa + PAGE_OFFSET, if the >> physical address is changed, we cannot simply update the kernel >> pagetable. On the contrary, we have to update all the pointers >> pointing to the virtual address, which is very difficult to do. >> > > It does beg the question if that "since" statement should be changed ... Do you mean we are going to do kernel page migration in the future ? > we already have it handled differently on Xen PV, but that is kind of > "special". There are a whole bunch of other issues with moving kernel > memory around: you have to worry what might have a physical address > cached somewhere and what might be in active use and so on... The current solution is to hotplug ZONE_MOVABLE, which the kernel won't use. So do you mean if I want to do kernel page migration (which I'm not doing), I need to worry about what you said above ? >I am not > really suggesting it as anything but food for thought at this time. Sorry for my poor English, and I really cannot understand this one. 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