Re: [PATCH RFC] mm/memory_hotplug: Introduce memory block types

From: David Hildenbrand <david@redhat.com>
To: "Michal Suchánek" <msuchanek@suse.de>
Cc: "Kate Stewart" <kstewart@linuxfoundation.org>,
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Subject: Re: [PATCH RFC] mm/memory_hotplug: Introduce memory block types
Date: Fri, 5 Oct 2018 09:37:39 +0200	[thread overview]
Message-ID: <a0739be1-564a-2853-c814-3290e64f24af@redhat.com> (raw)
In-Reply-To: <20181004195010.3616fc40@kitsune.suse.cz>

On 04/10/2018 19:50, Michal Suchánek wrote:
> On Thu, 4 Oct 2018 17:45:13 +0200
> David Hildenbrand <david@redhat.com> wrote:
> 
>> On 04/10/2018 17:28, Michal Suchánek wrote:
> 
>>>
>>> The state of the art is to determine what to do with hotplugged
>>> memory in userspace based on platform and virtualization type.  
>>
>> Exactly.
>>
>>>
>>> Changing the default to depend on the driver that added the memory
>>> rather than platform type should solve the issue of VMs growing
>>> different types of memory device emulation.  
>>
>> Yes, my original proposal (this patch) was to handle it in the kernel
>> for known types. But as we learned, there might be some use cases that
>> might still require to make a decision in user space.
>>
>> So providing the user space either with some type hint (auto-online
>> vs. standby) or the driver that added it (system vs. hyper-v ...)
>> would solve the issue.
> 
> Is that not available in the udev event?
> 

Not that I am aware. Memory blocks "devices" have no drivers.

ls -la /sys/devices/system/memory/memory0/subsystem/drivers
total 0

(add_memory()/add_memory_resource() creates the memory block devices
when called from a driver)

> Thanks
> 
> Michal
> 

-- 

Thanks,

David / dhildenb