Re: [PATCH 12/12] mm/memory_hotplug: drop CONFIG_HAVE_ARCH_PFN_VALID handling from pfn_to_online_page()

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Wed, Sep 09, 2026 at 03:33:05PM +0200, David Hildenbrand (Arm) wrote:
> Drop CONFIG_HAVE_ARCH_PFN_VALID handling, as CONFIG_HAVE_ARCH_PFN_VALID
> is never used with CONFIG_MEMORY_HOTPLUG, as the latter depends on
> CONFIG_SPARSEMEM_VMEMMAP. Make sure it stays that way.

So argument is:

mm/Makefile:

memory-hotplug-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o

Is memory_hotplug.c even compiled at all?

mm/Kconfig:

menuconfig MEMORY_HOTPLUG
	bool "Memory hotplug"
	select MEMORY_ISOLATION
	depends on SPARSEMEM_VMEMMAP
	depends on ARCH_ENABLE_MEMORY_HOTPLUG
	depends on 64BIT
	select NUMA_KEEP_MEMINFO if NUMA

$ cd arch
$ rg HAVE_ARCH_PFN_VALID
Kconfig
1762:config HAVE_ARCH_PFN_VALID

arm/Kconfig
94:	select HAVE_ARCH_PFN_VALID

arm/mm/init.c
121:#ifdef CONFIG_HAVE_ARCH_PFN_VALID

arm/include/asm/page.h
178:#ifdef CONFIG_HAVE_ARCH_PFN_VALID

m68k/Kconfig.cpu
23:	select HAVE_ARCH_PFN_VALID
40:	select HAVE_ARCH_PFN_VALID

arc/Kconfig
463:	select HAVE_ARCH_PFN_VALID

All of arm, m68k and arc are 32-bit arches so by definition MEMORY_HOTPLUG
can't be selected.

>
> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>

So LGTM and:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

> ---
>  mm/memory_hotplug.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b428da66d279c..58ce35cb48f57 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -344,6 +344,8 @@ struct page *pfn_to_online_page(unsigned long pfn)
>  	struct dev_pagemap *pgmap;
>  	struct mem_section *ms;
>
> +	BUILD_BUG_ON(IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID));

Haha nicest way of removing some later code I've seen. Just make it not compile
if such a thing happens :)

> +
>  	if (nr >= NR_MEM_SECTIONS)
>  		return NULL;
>
> @@ -351,13 +353,6 @@ struct page *pfn_to_online_page(unsigned long pfn)
>  	if (!online_section(ms))
>  		return NULL;
>
> -	/*
> -	 * Save some code text when online_section() +
> -	 * pfn_section_valid() are sufficient.
> -	 */
> -	if (IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID) && !pfn_valid(pfn))
> -		return NULL;
> -
>  	if (!pfn_section_valid(ms, pfn))
>  		return NULL;
>
>
> --
> 2.43.0
>

--
Cheers, Lorenzo