Subject: Re: [PATCH] powerpc/mm: update arch_{add,remove}_memory() for radix

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 23 Jun 2016 22:47:20 +0530

Reza Arbab <[email-masked]> writes:

> These functions are making direct calls to the hash table APIs,
> leading to a BUG() on systems using radix.
>
> Switch them to the vmemmap_{create,remove}_mapping() wrappers, and
> move to the __meminit section.

They are really not the same. They can possibly end up using different
base page size. Also vmemmap is available only with SPARSEMEM_VMEMMAP
enabled. Does hotplug depend on sparsemem vmemmap ?

>
> Signed-off-by: Reza Arbab <[email-masked]>
> ---
>  arch/powerpc/mm/mem.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index 2fd57fa..80c6ee7 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -116,7 +116,7 @@ int memory_add_physaddr_to_nid(u64 start)
>  }
>  #endif
>
> -int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
> +int __meminit arch_add_memory(int nid, u64 start, u64 size, bool for_device)
>  {
>  	struct pglist_data *pgdata;
>  	struct zone *zone;
> @@ -127,7 +127,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
>  	pgdata = NODE_DATA(nid);
>
>  	start = (unsigned long)__va(start);
> -	rc = create_section_mapping(start, start + size);
> +	rc = vmemmap_create_mapping(start, size, __pa(start));
>  	if (rc) {
>  		pr_warning(
>  			"Unable to create mapping for hot added memory 0x%llx..0x%llx: %d\n",
> @@ -143,7 +143,7 @@ int arch_add_memory(int nid, u64 start, u64 size, bool for_device)
>  }
>
>  #ifdef CONFIG_MEMORY_HOTREMOVE
> -int arch_remove_memory(u64 start, u64 size)
> +int __meminit arch_remove_memory(u64 start, u64 size)
>  {
>  	unsigned long start_pfn = start >> PAGE_SHIFT;
>  	unsigned long nr_pages = size >> PAGE_SHIFT;
> @@ -157,7 +157,7 @@ int arch_remove_memory(u64 start, u64 size)
>
>  	/* Remove htab bolted mappings for this section of memory */
>  	start = (unsigned long)__va(start);
> -	ret = remove_section_mapping(start, start + size);
> +	vmemmap_remove_mapping(start, size);
>
>  	/* Ensure all vmalloc mappings are flushed in case they also
>  	 * hit that section of memory
> -- 
> 1.8.3.1

We really want to look at memory hotplug to fully understand the
radix impact. The unplug operation needs to do some additional freeing.

I did put in comments around that with the idea of coming back to that
later

#ifdef CONFIG_MEMORY_HOTPLUG
void radix__vmemmap_remove_mapping(unsigned long start, unsigned long page_size)
{
	/* FIXME!! intel does more. We should free page tables mapping vmemmap ? */
}
#endif

-aneesh