linux-kernel - Re: [PATCH v3 1/5] mm,memory_hotplug: Introduce MHP_MEMMAP_ON

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Date:   Fri, 26 Jul 2019 11:37:07 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     akpm@...ux-foundation.org, dan.j.williams@...el.com,
        pasha.tatashin@...een.com, mhocko@...e.com,
        anshuman.khandual@....com, Jonathan.Cameron@...wei.com,
        vbabka@...e.cz, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/5] mm,memory_hotplug: Introduce MHP_MEMMAP_ON_MEMORY

>>
>>>
>>> or
>>> 	add_memory(0x1000, size_memory_block * 3);
>>>
>>> 	[memblock #0 ]
>>>         [0 - 1533 pfns    ] - vmemmap for section#{0-2}
>>>         [1534 - 98304 pfns] - normal memory
>>>
>>> When using larger memory blocks (1GB or 2GB), the principle is the same.
>>>
>>> Of course, per whole-range granularity is nicer when it comes to have a large
>>> contigous area, while per memory-block granularity allows us to have flexibility
>>> when removing the memory.
>>
>> E.g., in my virtio-mem I am currently adding all memory blocks
>> separately either way (to guranatee that remove_memory() works cleanly -
>> see __release_memory_resource()), and to control the amount of
>> not-offlined memory blocks (e.g., to make user space is actually
>> onlining them). As it's just a prototype, this might change of course in
>> the future.
> 
> What is virtio-mem for? Did it that raised from a need?
> Is it something you could try this patch on?

virtio-mem is a paravirtualized way of hotplugging/removing to/from a
guest. (similar to, but different to e.g., the hv-balloon). It
adds/removes memory to/from the system. In the long term, it will try to
also act similar-but different to a balloon - but that will require more
work. In the first shot, it's all about adding/removing memory in the
smaller granularity possible.

The old prototype was

https://lwn.net/Articles/755423/

Since then, a lot changed. Some more updated information is at

https://events.linuxfoundation.org/wp-content/uploads/2017/12/virtio-mem-Paravirtualized-Memory-David-Hildenbrand-Red-Hat-1.pdf

There is also a recording of the presentation on youtube.

The current prototype is unfortunately not in a state yet that allows me
to test with this patch set - my Master's thesis consumed most of my
energy during the last year. I just started hacking on it again.

-- 

Thanks,

David / dhildenb