[PATCH v2 4/8] riscv: mm: Add memory hotplugging support

[Oscar Salvador]

On Tue, May 14, 2024 at 04:04:42PM +0200, Björn Töpel wrote:
> +static void __meminit free_vmemmap_storage(struct page *page, size_t size,
> +					   struct vmem_altmap *altmap)
> +{
> +	if (altmap)
> +		vmem_altmap_free(altmap, size >> PAGE_SHIFT);
> +	else
> +		free_pages((unsigned long)page_address(page), get_order(size));

David already pointed this out, but can check
arch/x86/mm/init_64.c:free_pagetable().

You will see that we have to do some magic for bootmem memory (DIMMs
which were not hotplugged but already present)

> +#ifdef CONFIG_SPARSEMEM_VMEMMAP
> +void __ref vmemmap_free(unsigned long start, unsigned long end, struct vmem_altmap *altmap)
> +{
> +	remove_pgd_mapping(start, end, true, altmap);
> +}
> +#endif /* CONFIG_SPARSEMEM_VMEMMAP */
> +#endif /* CONFIG_MEMORY_HOTPLUG */

I will comment on the patch where you add support for hotplug and the
dependency, but on a track in LSFMM today, we decided that most likely
we will drop memory-hotplug support for !CONFIG_SPARSEMEM_VMEMMAP
environments.
So, since you are adding this plain fresh, please consider to tight the
hotplug dependency to CONFIG_SPARSEMEM_VMEMMAP.
As a bonus, you will only have to maintain one flavour of functions.


-- 
Oscar Salvador
SUSE Labs