Re: [PATCH v3 3/7] mm/hotplug: Allow architecture to override memmap on memory support check

[David Hildenbrand <david@redhat.com>]

On 11.07.23 18:07, Aneesh Kumar K V wrote:
> On 7/11/23 4:06 PM, David Hildenbrand wrote:
>> On 11.07.23 06:48, Aneesh Kumar K.V wrote:
>>> Some architectures would want different restrictions. Hence add an
>>> architecture-specific override.
>>>
>>> Both the PMD_SIZE check and pageblock alignment check are moved there.
>>>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>>> ---
>>>    mm/memory_hotplug.c | 17 ++++++++++++-----
>>>    1 file changed, 12 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>>> index 1b19462f4e72..07c99b0cc371 100644
>>> --- a/mm/memory_hotplug.c
>>> +++ b/mm/memory_hotplug.c
>>> @@ -1247,12 +1247,20 @@ static int online_memory_block(struct memory_block *mem, void *arg)
>>>        return device_online(&mem->dev);
>>>    }
>>>    -static bool mhp_supports_memmap_on_memory(unsigned long size)
>>> +#ifndef arch_supports_memmap_on_memory
>>
>> Can we make that a __weak function instead?
> 
> 
> We can. It is confusing because we do have these two patterns within the kernel where we use
> 
> #ifndef x
> #endif
> 
> vs
> 
> __weak x
> 
> What is the recommended way to override ? I have mostly been using #ifndef for most of the arch overrides till now.
> 

I think when placing the implementation in a C file, it's __weak. But 
don't ask me :)

We do this already for arch_get_mappable_range() in mm/memory_hotplug.c 
and IMHO it looks quite nice.


-- 
Cheers,

David / dhildenb