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

["David Hildenbrand (Arm)" <david@kernel.org>]

On 9/10/26 16:47, Lorenzo Stoakes (ARM) wrote:
> 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 :)

Better be safe than sorry :)

Thanks!

-- 
Cheers,

David