From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f177.google.com (mail-qk0-f177.google.com [209.85.220.177]) by kanga.kvack.org (Postfix) with ESMTP id DE41D6B0038 for ; Fri, 23 Oct 2015 14:36:27 -0400 (EDT) Received: by qkbl190 with SMTP id l190so85494225qkb.2 for ; Fri, 23 Oct 2015 11:36:27 -0700 (PDT) Received: from mail-qk0-x231.google.com (mail-qk0-x231.google.com. [2607:f8b0:400d:c09::231]) by mx.google.com with ESMTPS id b141si20066630qka.14.2015.10.23.11.36.27 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 23 Oct 2015 11:36:27 -0700 (PDT) Received: by qkfm62 with SMTP id m62so85359445qkf.1 for ; Fri, 23 Oct 2015 11:36:27 -0700 (PDT) Message-ID: <562a7e2a.4dc3370a.a30e5.ffff8e63@mx.google.com> Date: Fri, 23 Oct 2015 11:36:26 -0700 (PDT) From: Yasuaki Ishimatsu Subject: Re: [PATCH V7] mm: memory hot-add: memory can not be added to movable zone defaultly In-Reply-To: <5627586C.6000502@cn.fujitsu.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Tang Chen Cc: Vlastimil Babka , Changsheng Liu , akpm@linux-foundation.org, isimatu.yasuaki@jp.fujitsu.com, 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 Wed, 21 Oct 2015 17:18:36 +0800 Tang Chen wrote: > > On 10/21/2015 05:00 PM, Vlastimil Babka wrote: > > On 10/21/2015 04:20 AM, Changsheng Liu wrote: > >> > >> > >> a?? 2015/10/15 0:18, Vlastimil Babka a??e??: > >>> 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. I think the udev rules fails to online memory as movable. When hot adding memory, the memory is managed as ZONE_NORMAL. And add events of memory section are notified to udev in ascending order, like 0->1->2->3. Thus udev starts to online memory from section 0. But to change zone from ZONE_NORMAL to ZONE_MOVALBE, udev onlines memory in descending order, like 3->2->1->0. So the udev rules cannot online memory as movable. Thanks, Yasuaki Ishimatsu > > 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. > -- 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