From: Vlastimil Babka <vbabka@suse.cz>
To: Changsheng Liu <liuchangsheng@inspur.com>,
akpm@linux-foundation.org, isimatu.yasuaki@jp.fujitsu.com,
yasu.isimatu@gmail.com, tangchen@cn.fujitsu.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 <liuchangcheng@inspur.com>
Subject: Re: [PATCH V7] mm: memory hot-add: memory can not be added to movable zone defaultly
Date: Wed, 21 Oct 2015 11:00:19 +0200 [thread overview]
Message-ID: <56275423.6050506@suse.cz> (raw)
In-Reply-To: <5626F667.9000003@inspur.com>
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 <liuchangcheng@inspur.com>
>>>
>>> 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...
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next prev parent reply other threads:[~2015-10-21 9:00 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-12 6:58 [PATCH V7] mm: memory hot-add: memory can not be added to movable zone defaultly Changsheng Liu
2015-10-14 16:18 ` Vlastimil Babka
2015-10-21 2:20 ` Changsheng Liu
2015-10-21 9:00 ` Vlastimil Babka [this message]
2015-10-21 9:18 ` Tang Chen
2015-10-21 9:20 ` Tang Chen
2015-10-23 18:36 ` Yasuaki Ishimatsu
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