From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx206.postini.com [74.125.245.206]) by kanga.kvack.org (Postfix) with SMTP id 94BEB6B0031 for ; Mon, 5 Aug 2013 09:08:35 -0400 (EDT) Message-ID: <51FFA393.2080301@zytor.com> Date: Mon, 05 Aug 2013 06:07:31 -0700 From: "H. Peter Anvin" 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> In-Reply-To: <1375340800-19332-1-git-send-email-tangchen@cn.fujitsu.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Tang Chen 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 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 ... 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... I am not really suggesting it as anything but food for thought at this time. -hpa -- 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