From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f52.google.com (mail-pa0-f52.google.com [209.85.220.52]) by kanga.kvack.org (Postfix) with ESMTP id EE6CC6B0256 for ; Wed, 21 Oct 2015 05:22:34 -0400 (EDT) Received: by pabrc13 with SMTP id rc13so49770543pab.0 for ; Wed, 21 Oct 2015 02:22:34 -0700 (PDT) Received: from heian.cn.fujitsu.com ([59.151.112.132]) by mx.google.com with ESMTP id hx4si11981933pac.153.2015.10.21.02.22.33 for ; Wed, 21 Oct 2015 02:22:34 -0700 (PDT) Message-ID: <562758EC.7050208@cn.fujitsu.com> Date: Wed, 21 Oct 2015 17:20:44 +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> <5627586C.6000502@cn.fujitsu.com> In-Reply-To: <5627586C.6000502@cn.fujitsu.com> 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 05:18 PM, Tang Chen wrote: > > 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=20 >>>>> 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=20 > default. If users use a udev rule as below: > > SUBSYSTEM=3D=3D"memory", ACTION=3D=3D"add", ATTR{state}=3D=3D"offline",=20 > ATTR{state}=3D"online" > > it will online the memory as normal memory, which will not be=20 > 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=20 > this work ? sorry, I'm NOT quite familiar with udev rules, ...... > > SUBSYSTEM=3D=3D"memory", ACTION=3D=3D"add", ATTR{state}=3D=3D"offline",=20 > ATTR{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.=20 > If 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. > > --=20 > To unsubscribe from this list: send the line "unsubscribe=20 > linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > . > -- 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