[v1] mm: memory hot(un)plug and SPARSEMEM cleanups

[PATCH 11/14] mm/sparse: drop set_section_nid() from sparse_add_section()

Posted by David Hildenbrand (Arm) 2 weeks, 6 days ago

CONFIG_MEMORY_HOTPLUG is CONFIG_SPARSEMEM_VMEMMAP-only. And
CONFIG_SPARSEMEM_VMEMMAP implies that NODE_NOT_IN_PAGE_FLAGS cannot be set:
see include/linux/page-flags-layout.h

	...
	#elif defined(CONFIG_SPARSEMEM_VMEMMAP)
	#error "Vmemmap: No space for nodes field in page flags"
	...

So let's remove the set_section_nid() call to prepare for moving
CONFIG_MEMORY_HOTPLUG to mm/sparse-vmemmap.c

Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/sparse.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 7b0bfea73a9b..b5a2de43ac40 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -769,7 +769,6 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
 	page_init_poison(memmap, sizeof(struct page) * nr_pages);
 
 	ms = __nr_to_section(section_nr);
-	set_section_nid(section_nr, nid);
 	__section_mark_present(ms, section_nr);
 
 	/* Align memmap to section boundary in the subsection case */
-- 
2.43.0

Re: [PATCH 11/14] mm/sparse: drop set_section_nid() from sparse_add_section()

Posted by Mike Rapoport 2 weeks, 5 days ago

On Tue, Mar 17, 2026 at 05:56:49PM +0100, David Hildenbrand (Arm) wrote:
> CONFIG_MEMORY_HOTPLUG is CONFIG_SPARSEMEM_VMEMMAP-only. And
> CONFIG_SPARSEMEM_VMEMMAP implies that NODE_NOT_IN_PAGE_FLAGS cannot be set:

Maybe 

... implies that node is always in page flags and NODE_NOT_IN_PAGE_FLAGS
cannot be set

> see include/linux/page-flags-layout.h
> 
> 	...
> 	#elif defined(CONFIG_SPARSEMEM_VMEMMAP)
> 	#error "Vmemmap: No space for nodes field in page flags"
> 	...
> 
> So let's remove the set_section_nid() call to prepare for moving
> CONFIG_MEMORY_HOTPLUG to mm/sparse-vmemmap.c
> 
> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
>  mm/sparse.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 7b0bfea73a9b..b5a2de43ac40 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -769,7 +769,6 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>  	page_init_poison(memmap, sizeof(struct page) * nr_pages);
>  
>  	ms = __nr_to_section(section_nr);
> -	set_section_nid(section_nr, nid);
>  	__section_mark_present(ms, section_nr);
>  
>  	/* Align memmap to section boundary in the subsection case */
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH 11/14] mm/sparse: drop set_section_nid() from sparse_add_section()

Posted by Lorenzo Stoakes (Oracle) 2 weeks, 6 days ago

On Tue, Mar 17, 2026 at 05:56:49PM +0100, David Hildenbrand (Arm) wrote:
> CONFIG_MEMORY_HOTPLUG is CONFIG_SPARSEMEM_VMEMMAP-only. And
> CONFIG_SPARSEMEM_VMEMMAP implies that NODE_NOT_IN_PAGE_FLAGS cannot be set:
> see include/linux/page-flags-layout.h
>
> 	...
> 	#elif defined(CONFIG_SPARSEMEM_VMEMMAP)
> 	#error "Vmemmap: No space for nodes field in page flags"
> 	...
>
> So let's remove the set_section_nid() call to prepare for moving
> CONFIG_MEMORY_HOTPLUG to mm/sparse-vmemmap.c
>

Maybe worth mentioning:

#ifdef NODE_NOT_IN_PAGE_FLAGS
...
static void set_section_nid(unsigned long section_nr, int nid)
{
	... actually does something ...
}
#else /* !NODE_NOT_IN_PAGE_FLAGS */
static inline void set_section_nid(unsigned long section_nr, int nid)
{
}
#endif

Or more succintly 'set_section_nid() is a nop' or something :P

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

You may have dropped the call, but you've not dropped the ball, so:

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

> ---
>  mm/sparse.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 7b0bfea73a9b..b5a2de43ac40 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -769,7 +769,6 @@ int __meminit sparse_add_section(int nid, unsigned long start_pfn,
>  	page_init_poison(memmap, sizeof(struct page) * nr_pages);
>
>  	ms = __nr_to_section(section_nr);
> -	set_section_nid(section_nr, nid);
>  	__section_mark_present(ms, section_nr);
>
>  	/* Align memmap to section boundary in the subsection case */
> --
> 2.43.0
>