From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f181.google.com (mail-io0-f181.google.com [209.85.223.181]) by kanga.kvack.org (Postfix) with ESMTP id 6D58A6B0256 for ; Wed, 21 Oct 2015 05:21:30 -0400 (EDT) Received: by iofz202 with SMTP id z202so50667940iof.2 for ; Wed, 21 Oct 2015 02:21:30 -0700 (PDT) Received: from heian.cn.fujitsu.com ([59.151.112.132]) by mx.google.com with ESMTP id y101si6523618ioi.210.2015.10.21.02.21.27 for ; Wed, 21 Oct 2015 02:21:29 -0700 (PDT) Message-ID: <5627586C.6000502@cn.fujitsu.com> Date: Wed, 21 Oct 2015 17:18:36 +0800 From: Tang Chen MIME-Version: 1.0 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: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Vlastimil Babka , Changsheng Liu , akpm@linux-foundation.org, isimatu.yasuaki@jp.fujitsu.com, yasu.isimatu@gmail.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, wangnan0@huawei.com, dave.hansen@intel.com, yinghai@kernel.org, toshi.kani@hp.com, qiuxishi@huawei.com, wunan@inspur.com, yanxiaofeng@inspur.com, fandd@inspur.com, Changsheng Liu On 10/21/2015 05:00 PM, Vlastimil Babka wrote: > On 10/21/2015 04:20 AM, Changsheng Liu wrote: >> >> >> =E5=9C=A8 2015/10/15 0:18, Vlastimil Babka =E5=86=99=E9=81=93: >>> 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=3D=3D"memory", ACTION=3D=3D"add", >>>> ATTR{state}=3D=3D"offline", ATTR{state}=3D"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=20 >>> movable_node_is_enabled(), and >>> does the same thing for non-hot-added-memory (?) cannot be reused=20 >>> for hot-added >>> memory, as that would be a potentially surprising behavior change?=20 >>> Correct? Then >>> this should be mentioned in the changelog too, and wherever=20 >>> "movable_node" is >>> documented should also mention the new sysctl. Personally, I would=20 >>> expect >>> movable_node to affect hot-added memory as well, and would be=20 >>> 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=20 >> next >> node to ZONE_NORMAL . > > So you mean sysctl is more flexible than boot option. OK, but wasn't=20 > such flexibility already provided by "echo online_kernel" vs "echo=20 > online_movable"? It doesn't sound like a strong reason for a new=20 > sysctl? Not doing surprising behavior change maybe does... > . > Hi Vlastimil, The current kernel will add hot-added memory to ZONE_NORMAL by default.=20 If users use a udev rule as below: SUBSYSTEM=3D=3D"memory", ACTION=3D=3D"add", ATTR{state}=3D=3D"offline", ATT= R{state}=3D"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=20 work ? SUBSYSTEM=3D=3D"memory", ACTION=3D=3D"add", ATTR{state}=3D=3D"offline", ATT= R{state}=3D"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=20 not, maybe we should just change the kernel behavior to make the=20 hot-added memory be added to ZONE_MOVABLE by default. I don't have objection. But a sysctl doesn't sound necessary. 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