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 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?

> +static inline bool arch_supports_memmap_on_memory(unsigned long size)
>   {
> -	unsigned long nr_vmemmap_pages = size / PAGE_SIZE;
> +	unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
>   	unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
>   	unsigned long remaining_size = size - vmemmap_size;
>   
> +	return IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
> +		IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));

You're moving that check back to mhp_supports_memmap_on_memory() in the 
following patch, where it actually belongs. So this check should stay in 
mhp_supports_memmap_on_memory(). Might be reasonable to factor out the 
vmemmap_size calculation.


Also, let's a comment

/*
  * As default, we want the vmemmap to span a complete PMD such that we
  * can map the vmemmap using a single PMD if supported by the
  * architecture.
  */
return IS_ALIGNED(vmemmap_size, PMD_SIZE);

> +}
> +#endif
> +
> +static bool mhp_supports_memmap_on_memory(unsigned long size)
> +{
>   	/*
>   	 * Besides having arch support and the feature enabled at runtime, we
>   	 * need a few more assumptions to hold true:
> @@ -1280,9 +1288,8 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
>   	 *       populate a single PMD.
>   	 */
>   	return mhp_memmap_on_memory() &&
> -	       size == memory_block_size_bytes() &&
> -	       IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
> -	       IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
> +		size == memory_block_size_bytes() &&

If you keep the properly aligned indentation, this will not be detected 
as a change by git.

> +		arch_supports_memmap_on_memory(size);
>   }
>   
>   /*

-- 
Cheers,

David / dhildenb