From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753979AbbJUJUc (ORCPT ); Wed, 21 Oct 2015 05:20:32 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:13644 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1753147AbbJUJU2 convert rfc822-to-8bit (ORCPT ); Wed, 21 Oct 2015 05:20:28 -0400 X-IronPort-AV: E=Sophos;i="5.15,520,1432569600"; d="scan'208";a="102099127" Message-ID: <5627586C.6000502@cn.fujitsu.com> Date: Wed, 21 Oct 2015 17:18:36 +0800 From: Tang Chen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Vlastimil Babka , Changsheng Liu , , , CC: , , , , , , , , , , Changsheng Liu , Yasuaki Ishimatsu Subject: Re: [PATCH V7] mm: memory hot-add: memory can not be added to movable zone defaultly References: <1444633113-27607-1-git-send-email-liuchangsheng@inspur.com> <561E8056.7050609@suse.cz> <5626F667.9000003@inspur.com> <56275423.6050506@suse.cz> In-Reply-To: <56275423.6050506@suse.cz> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/21/2015 05:00 PM, Vlastimil Babka wrote: > On 10/21/2015 04:20 AM, Changsheng Liu wrote: >> >> >> 在 2015/10/15 0:18, Vlastimil Babka 写道: >>> On 10/12/2015 08:58 AM, Changsheng Liu wrote: >>>> From: Changsheng Liu >>>> >>>> After the user config CONFIG_MOVABLE_NODE, >>>> When the memory is hot added, should_add_memory_movable() return 0 >>>> because all zones including ZONE_MOVABLE are empty, >>>> so the memory that was hot added will be assigned to ZONE_NORMAL >>>> and ZONE_NORMAL will be created firstly. >>>> But we want the whole node to be added to ZONE_MOVABLE by default. >>>> >>>> So we change should_add_memory_movable(): if the user config >>>> CONFIG_MOVABLE_NODE and sysctl parameter hotadd_memory_as_movable is 1 >>>> and the ZONE_NORMAL is empty or the pfn of the hot-added memory >>>> is after the end of the ZONE_NORMAL it will always return 1 >>>> and then the whole node will be added to ZONE_MOVABLE by default. >>>> If we want the node to be assigned to ZONE_NORMAL, >>>> we can do it as follows: >>>> "echo online_kernel > /sys/devices/system/memory/memoryXXX/state" >>>> >>>> By the patch, the behavious of kernel is changed by sysctl, >>>> user can automatically create movable memory >>>> by only the following udev rule: >>>> SUBSYSTEM=="memory", ACTION=="add", >>>> ATTR{state}=="offline", ATTR{state}="online" >> I'm sorry for replying you so late due to the busy business trip. >>> So just to be clear, we are adding a new sysctl, because the existing >>> movable_node kernel option, which is checked by >>> movable_node_is_enabled(), and >>> does the same thing for non-hot-added-memory (?) cannot be reused >>> for hot-added >>> memory, as that would be a potentially surprising behavior change? >>> Correct? Then >>> this should be mentioned in the changelog too, and wherever >>> "movable_node" is >>> documented should also mention the new sysctl. Personally, I would >>> expect >>> movable_node to affect hot-added memory as well, and would be >>> surprised that it >>> doesn't... >> I think it can let the user decides when to use this feature. >> The user can enable the feature when making the hot_added memory >> of a node movable and >> make the feature disable to assign the hot_added memory of the >> next >> node to ZONE_NORMAL . > > So you mean sysctl is more flexible than boot option. OK, but wasn't > such flexibility already provided by "echo online_kernel" vs "echo > online_movable"? It doesn't sound like a strong reason for a new > sysctl? Not doing surprising behavior change maybe does... > . > Hi Vlastimil, The current kernel will add hot-added memory to ZONE_NORMAL by default. If users use a udev rule as below: SUBSYSTEM=="memory", ACTION=="add", ATTR{state}=="offline", ATTR{state}="online" it will online the memory as normal memory, which will not be hotpluggable. Please refer to: https://lkml.org/lkml/2015/10/9/58 I think this is the root motivation of the patch. But BTW, I'm quite familiar with udev rules, but can something like this work ? SUBSYSTEM=="memory", ACTION=="add", ATTR{state}=="offline", ATTR{state}="online_movable" I'm not sure. I added Ishimatu in. For now, I think, if the above rule works, we don't need this patch. If not, maybe we should just change the kernel behavior to make the hot-added memory be added to ZONE_MOVABLE by default. I don't have objection. But a sysctl doesn't sound necessary. Thanks.