[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v2 2/3] mm/memory_hotplug: Introduce MHP_NO_FIRMWARE_MEMMAP


  • To: Dan Williams <dan.j.williams@xxxxxxxxx>
  • From: David Hildenbrand <david@xxxxxxxxxx>
  • Date: Fri, 1 May 2020 19:21:15 +0200
  • Autocrypt: addr=david@xxxxxxxxxx; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg=
  • Cc: virtio-dev@xxxxxxxxxxxxxxxxxxxx, linux-hyperv@xxxxxxxxxxxxxxx, Michal Hocko <mhocko@xxxxxxxx>, Baoquan He <bhe@xxxxxxxxxx>, Linux ACPI <linux-acpi@xxxxxxxxxxxxxxx>, Wei Yang <richard.weiyang@xxxxxxxxx>, linux-s390 <linux-s390@xxxxxxxxxxxxxxx>, linux-nvdimm <linux-nvdimm@xxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, Linux MM <linux-mm@xxxxxxxxx>, "Michael S . Tsirkin" <mst@xxxxxxxxxx>, "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>, Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Michal Hocko <mhocko@xxxxxxxxxx>, linuxppc-dev <linuxppc-dev@xxxxxxxxxxxxxxxx>
  • Delivery-date: Fri, 01 May 2020 17:21:52 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 01.05.20 18:56, Dan Williams wrote:
> On Fri, May 1, 2020 at 2:34 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
>>
>> On 01.05.20 00:24, Andrew Morton wrote:
>>> On Thu, 30 Apr 2020 20:43:39 +0200 David Hildenbrand <david@xxxxxxxxxx> 
>>> wrote:
>>>
>>>>>
>>>>> Why does the firmware map support hotplug entries?
>>>>
>>>> I assume:
>>>>
>>>> The firmware memmap was added primarily for x86-64 kexec (and still, is
>>>> mostly used on x86-64 only IIRC). There, we had ACPI hotplug. When DIMMs
>>>> get hotplugged on real HW, they get added to e820. Same applies to
>>>> memory added via HyperV balloon (unless memory is unplugged via
>>>> ballooning and you reboot ... the the e820 is changed as well). I assume
>>>> we wanted to be able to reflect that, to make kexec look like a real 
>>>> reboot.
>>>>
>>>> This worked for a while. Then came dax/kmem. Now comes virtio-mem.
>>>>
>>>>
>>>> But I assume only Andrew can enlighten us.
>>>>
>>>> @Andrew, any guidance here? Should we really add all memory to the
>>>> firmware memmap, even if this contradicts with the existing
>>>> documentation? (especially, if the actual firmware memmap will *not*
>>>> contain that memory after a reboot)
>>>
>>> For some reason that patch is misattributed - it was authored by
>>> Shaohui Zheng <shaohui.zheng@xxxxxxxxx>, who hasn't been heard from in
>>> a decade.  I looked through the email discussion from that time and I'm
>>> not seeing anything useful.  But I wasn't able to locate Dave Hansen's
>>> review comments.
>>
>> Okay, thanks for checking. I think the documentation from 2008 is pretty
>> clear what has to be done here. I will add some of these details to the
>> patch description.
>>
>> Also, now that I know that esp. kexec-tools already don't consider
>> dax/kmem memory properly (memory will not get dumped via kdump) and
>> won't really suffer from a name change in /proc/iomem, I will go back to
>> the MHP_DRIVER_MANAGED approach and
>> 1. Don't create firmware memmap entries
>> 2. Name the resource "System RAM (driver managed)"
>> 3. Flag the resource via something like IORESOURCE_MEM_DRIVER_MANAGED.
>>
>> This way, kernel users and user space can figure out that this memory
>> has different semantics and handle it accordingly - I think that was
>> what Eric was asking for.
>>
>> Of course, open for suggestions.
> 
> I'm still more of a fan of this being communicated by "System RAM"

I was mentioning somewhere in this thread that "System RAM" inside a
hierarchy (like dax/kmem) will already be basically ignored by
kexec-tools. So, placing it inside a hierarchy already makes it look
special already.

But after all, as we have to change kexec-tools either way, we can
directly go ahead and flag it properly as special (in case there will
ever be other cases where we could no longer distinguish it).

> being parented especially because that tells you something about how
> the memory is driver-managed and which mechanism might be in play.

The could be communicated to some degree via the resource hierarchy.

E.g.,

            [root@localhost ~]# cat /proc/iomem
            ...
            140000000-33fffffff : Persistent Memory
              140000000-1481fffff : namespace0.0
              150000000-33fffffff : dax0.0
                150000000-33fffffff : System RAM (driver managed)

vs.

           :/# cat /proc/iomem
            [...]
            140000000-333ffffff : virtio-mem (virtio0)
              140000000-147ffffff : System RAM (driver managed)
              148000000-14fffffff : System RAM (driver managed)
              150000000-157ffffff : System RAM (driver managed)

Good enough for my taste.

> What about adding an optional /sys/firmware/memmap/X/parent attribute.

I really don't want any firmware memmap entries for something that is
not part of the firmware provided memmap. In addition,
/sys/firmware/memmap/ is still a fairly x86_64 specific thing. Only mips
and two arm configs enable it at all.

So, IMHO, /sys/firmware/memmap/ is definitely not the way to go.

-- 
Thanks,

David / dhildenb




 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.