Re: [PATCH v2 3/8] mm/memory_hotplug: arch_remove_memory() and __remove_pages() with CONFIG_MEMORY_HOTPLUG

From: David Hildenbrand <david@redhat.com>
To: Dan Williams <dan.j.williams@intel.com>,
	Michal Hocko <mhocko@suse.com>,
	Oscar Salvador <osalvador@suse.com>
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Subject: Re: [PATCH v2 3/8] mm/memory_hotplug: arch_remove_memory() and __remove_pages() with CONFIG_MEMORY_HOTPLUG
Date: Mon, 13 May 2019 10:20:43 +0200	[thread overview]
Message-ID: <fd061541-4433-d7a2-df73-66f39b61d0c9@redhat.com> (raw)
In-Reply-To: <c027a782-1cef-a076-92a3-3ce36140f3f2@redhat.com>

On 13.05.19 09:48, David Hildenbrand wrote:
> On 07.05.19 23:02, Dan Williams wrote:
>> On Tue, May 7, 2019 at 11:38 AM David Hildenbrand <david@redhat.com> wrote:
>>>
>>> Let's prepare for better error handling while adding memory by allowing
>>> to use arch_remove_memory() and __remove_pages() even if
>>> CONFIG_MEMORY_HOTREMOVE is not set. CONFIG_MEMORY_HOTREMOVE effectively
>>> covers
>>> - Offlining of system ram (memory block devices) - offline_pages()
>>> - Unplug of system ram - remove_memory()
>>> - Unplug/remap of device memory - devm_memremap()
>>>
>>> This allows e.g. for handling like
>>>
>>> arch_add_memory()
>>> rc = do_something();
>>> if (rc) {
>>>         arch_remove_memory();
>>> }
>>>
>>> Whereby do_something() will for example be memory block device creation
>>> after it has been factored out.
>>
>> What's left after this? Can we just get rid of CONFIG_MEMORY_HOTREMOVE
>> option completely when CONFIG_MEMORY_HOTPLUG is enabled? It's not
>> clear to me why there was ever the option to compile out the remove
>> code when the add code is included.
>>
> 
> If there are no other comments, I will go ahead and rip out
> CONFIG_MEMORY_HOTREMOVE completely, gluing the functionality to
> CONFIG_MEMORY_HOTPLUG.
> 

Hmmmm, however this will require CONFIG_MEMORY_HOTPLUG to require

- MEMORY_ISOLATION
- HAVE_BOOTMEM_INFO_NODE if (X86_64 || PPC64)

And depends on
- MIGRATION

Which would limit the configurations where memory hotplug would be
available. I guess going with this patch here is ok as a first step.

I just realized, that we'll need arch_remove_memory() for arm64 to make
this patch here work.

-- 

Thanks,

David / dhildenb