On 2015/12/16 17:17, Vitaly Kuznetsov wrote:
> Xishi Qiu <qiuxi...@huawei.com> writes:
>
>> On 2015/12/16 2:05, Vitaly Kuznetsov wrote:
>>
>>> Currently, all newly added memory blocks remain in 'offline' state unless
>>> someone onlines them, some linux distributions carry special udev rules
>>> like:
>>>
>>> SUBSYSTEM=="memory", ACTION=="add", ATTR{state}=="offline",
>>> ATTR{state}="online"
>>>
>>> to make this happen automatically. This is not a great solution for virtual
>>> machines where memory hotplug is being used to address high memory pressure
>>> situations as such onlining is slow and a userspace process doing this
>>> (udev) has a chance of being killed by the OOM killer as it will probably
>>> require to allocate some memory.
>>>
>>> Introduce default policy for the newly added memory blocks in
>>> /sys/devices/system/memory/hotplug_autoonline file with two possible
>>> values: "offline" (the default) which preserves the current behavior and
>>> "online" which causes all newly added memory blocks to go online as
>>> soon as they're added.
>>>
>>> Cc: Jonathan Corbet <cor...@lwn.net>
>>> Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
>>> Cc: Daniel Kiper <daniel.ki...@oracle.com>
>>> Cc: Dan Williams <dan.j.willi...@intel.com>
>>> Cc: Tang Chen <tangc...@cn.fujitsu.com>
>>> Cc: David Vrabel <david.vra...@citrix.com>
>>> Cc: David Rientjes <rient...@google.com>
>>> Cc: Andrew Morton <a...@linux-foundation.org>
>>> Cc: Naoya Horiguchi <n-horigu...@ah.jp.nec.com>
>>> Cc: Gu Zheng <guz.f...@cn.fujitsu.com>
>>> Cc: Xishi Qiu <qiuxi...@huawei.com>
>>> Cc: Mel Gorman <mgor...@techsingularity.net>
>>> Cc: "K. Y. Srinivasan" <k...@microsoft.com>
>>> Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
>>> ---
>>> - I was able to find previous attempts to fix the issue, e.g.:
>>> http://marc.info/?l=linux-kernel&m=137425951924598&w=2
>>> http://marc.info/?l=linux-acpi&m=127186488905382
>>> but I'm not completely sure why it didn't work out and the solution
>>> I suggest is not 'smart enough', thus 'RFC'.
>>
>> + CC:
>> yanxiaof...@inspur.com
>> liuchangsh...@inspur.com
>>
>> Hi Vitaly,
>>
>> Why not use udev rule? I think it can online pages automatically.
>>
>
> Two main reasons:
> 1) I remember someone saying "You never need a mouse in order to add
> another mouse to the kernel" -- but we we need memory to add more
> memory. Udev has a chance of being killed by the OOM killer as
> performing an action will probably require to allocate some
> memory. Other than that udev actions are generally slow compared to what
> we can do in kernel.
Hi Vitaly,
So why we add memory when there is almost no free memory left?
I think the administrator should add memory when the free memory is low
or he should do something to stop free memory become worse.
>
> 2) I agree with Kay that '... unconditional hotplug loop through
> userspace is absolutely pointless' (https://lkml.org/lkml/2013/7/25/354).
> (... and I should had add him to CC, adding now). Udev maintainers
> refused to add a rule for unconditional memory onlining to udev and now
> linux distros have to carry such custom rules.
>
If the administrator don't know how to config the udev, he could use sysfs
(echo 1 > /sys/devices/system/node/nodeXX/memoryXX/online) to online it,
or write a script to do this.
Thanks,
Xishi Qiu
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