linux-kernel - Re: [PATCH v1] memory-hotplug.rst: complete admin-guide overhaul

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Date:   Tue, 8 Jun 2021 17:22:10 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Muchun Song <songmuchun@...edance.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Jonathan Corbet <corbet@....net>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v1] memory-hotplug.rst: complete admin-guide overhaul


Looks like a was too fast with my resend ;)

>>>> -Phases of memory hotplug
>>>> +Further, the basic memory hot(un)plug infrastructure in Linux is nowadays
>>>> +also used to expose PMEM, other performance-differentiated
>>>
>>>                         ^ persistent memory (PMEM)
>>>
> 
> Just in case you've missed this one ^ ;-)

I did catch that :)

[...]

>>
>> "If it fails, an error will be returned by the kernel via the systemcall
>> that triggered modifying of the respective file."
> 
> I also think that write(2) to /sys/devices/system/memory/memoryXXX/online
> will fail.  But the inner workings of system call, its return value and the
> ERRNO are probably not very interesting to a person that did
> 
> echo 0 > /sys/devices/system/memory/memoryXXX/online
> 
> Maybe something like
> 
>    If it fails, the state of the memory block will remain unchanged and the
>    above command will fail.

Thanks, I'll use that.

> 
> And maybe an example of how echo reports some unrelated error message :)
> 
>>>> +Observing the State of Memory Blocks
> 
> ...
> 
>>>> -Now, a boot option for making a memory block which consists of migratable pages
>>>> -is supported. By specifying "kernelcore=" or "movablecore=" boot option, you can
>>>> -create ZONE_MOVABLE...a zone which is just used for movable pages.
>>>> -(See also Documentation/admin-guide/kernel-parameters.rst)
>>>> +		    For online memory blocks, ``DMA``, ``DMA32``, ``Normal``,
>>>> +		    ``Movable`` and ``none`` may be returned. ``none`` indicates
>>>
>>> Highmem? Or we don't support hotplug on 32 bits?
>>
>> We only support 64 bit:
>>
>> config MEMORY_HOTPLUG
>> 	...
>> 	depends on 64BIT || BROKEN
>>
>> Worth a comment in the document "Introduction":
>>
>> "Linux only supports memory hot(un)plug on selected 64 bit architectures,
>> such as x86_64, aarch64, ppc64, s390x and ia64."
>   
>                   ^ arm64 ?

I think aarch64 is historically actually the right(tm) thing to use in 
general ... but nowadays it doesn't matter anymore. It's "arch/arm64" 
... the inconsistency is real. (interesting read: 
https://stackoverflow.com/questions/31851611/differences-between-arm64-and-aarch64)

But it's the same mess as using x86 vs. x86_64 vs. x64 vs. AMD64 for the 
64 bit extension of IA-32.

So I'll convert that to arm64.

-- 
Thanks,

David / dhildenb