linux-kernel - Re: [RFC PATCH v3 1/4] mm,memory_hotplug: Add mhp_supports_memmap_on

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Message-ID: <5809e56e-363b-abe4-7b95-08768c6a4b32@redhat.com>
Date:   Wed, 9 Dec 2020 10:40:13 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     mhocko@...nel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, vbabka@...e.cz, pasha.tatashin@...een.com
Subject: Re: [RFC PATCH v3 1/4] mm,memory_hotplug: Add
 mhp_supports_memmap_on_memory

On 09.12.20 10:36, Oscar Salvador wrote:
> On Wed, Dec 02, 2020 at 10:36:54AM +0100, David Hildenbrand wrote:
>> Instead of adding these arch callbacks, what about a config option
>>
>> ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
>>
>> that gets selected by the archs with CONFIG_SPARSEMEM_VMEMMAP ?
>>
>> The mhp_supports_memmap_on_memory() becomes even more trivial.
> 
> I think that would not be enough.
> E.g: s390x supports CONFIG_SPARSEMEM_VMEMMAP but it does not support
> altmap (and maybe other arches I did not check too).
> That is why I was careful in choosing the ones that a) supports
> CONFIG_SPARSEMEM_VMEMMAP and b) support altmap

Sorry if I was unclear, s390x will simply not set
ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE.

-- 
Thanks,

David / dhildenb