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[PATCH v2 13/15] mm/sparse: move sparse_init_one_section() to internal.h

David Hildenbrand (Arm) posted 15 patches 2 weeks ago
[PATCH v2 13/15] mm/sparse: move sparse_init_one_section() to internal.h
Posted by David Hildenbrand (Arm) 2 weeks ago 
While at it, convert the BUG_ON to a VM_WARN_ON_ONCE, avoid long lines, and
merge sparse_encode_mem_map() into its only caller
sparse_init_one_section().

Clarify the comment a bit, pointing at page_to_pfn().

Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 include/linux/mmzone.h |  2 +-
 mm/internal.h          | 22 ++++++++++++++++++++++
 mm/sparse.c            | 24 ------------------------
 3 files changed, 23 insertions(+), 25 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index b694c69dee04..dcbbf36ed88c 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -2008,7 +2008,7 @@ struct mem_section {
 	/*
 	 * This is, logically, a pointer to an array of struct
 	 * pages.  However, it is stored with some other magic.
-	 * (see sparse.c::sparse_init_one_section())
+	 * (see sparse_init_one_section())
 	 *
 	 * Additionally during early boot we encode node id of
 	 * the location of the section here to guide allocation.
diff --git a/mm/internal.h b/mm/internal.h
index 5f5c45d80aca..2f188f7702f7 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -965,6 +965,28 @@ void memmap_init_range(unsigned long, int, unsigned long, unsigned long,
  */
 #ifdef CONFIG_SPARSEMEM
 void sparse_init(void);
+
+static inline void sparse_init_one_section(struct mem_section *ms,
+		unsigned long pnum, struct page *mem_map,
+		struct mem_section_usage *usage, unsigned long flags)
+{
+	unsigned long coded_mem_map;
+
+	BUILD_BUG_ON(SECTION_MAP_LAST_BIT > PFN_SECTION_SHIFT);
+
+	/*
+	 * We encode the start PFN of the section into the mem_map such that
+	 * page_to_pfn() on !CONFIG_SPARSEMEM_VMEMMAP can simply subtract it
+	 * from the page pointer to obtain the PFN.
+	 */
+	coded_mem_map = (unsigned long)(mem_map - section_nr_to_pfn(pnum));
+	VM_WARN_ON(coded_mem_map & ~SECTION_MAP_MASK);
+
+	ms->section_mem_map &= ~SECTION_MAP_MASK;
+	ms->section_mem_map |= coded_mem_map;
+	ms->section_mem_map |= flags | SECTION_HAS_MEM_MAP;
+	ms->usage = usage;
+}
 #else
 static inline void sparse_init(void) {}
 #endif /* CONFIG_SPARSEMEM */
diff --git a/mm/sparse.c b/mm/sparse.c
index 5c9cad390282..ed5de1a25f04 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -256,30 +256,6 @@ static void __init memblocks_present(void)
 		memory_present(nid, start, end);
 }
 
-/*
- * Subtle, we encode the real pfn into the mem_map such that
- * the identity pfn - section_mem_map will return the actual
- * physical page frame number.
- */
-static unsigned long sparse_encode_mem_map(struct page *mem_map, unsigned long pnum)
-{
-	unsigned long coded_mem_map =
-		(unsigned long)(mem_map - (section_nr_to_pfn(pnum)));
-	BUILD_BUG_ON(SECTION_MAP_LAST_BIT > PFN_SECTION_SHIFT);
-	BUG_ON(coded_mem_map & ~SECTION_MAP_MASK);
-	return coded_mem_map;
-}
-
-static void __meminit sparse_init_one_section(struct mem_section *ms,
-		unsigned long pnum, struct page *mem_map,
-		struct mem_section_usage *usage, unsigned long flags)
-{
-	ms->section_mem_map &= ~SECTION_MAP_MASK;
-	ms->section_mem_map |= sparse_encode_mem_map(mem_map, pnum)
-		| SECTION_HAS_MEM_MAP | flags;
-	ms->usage = usage;
-}
-
 static unsigned long usemap_size(void)
 {
 	return BITS_TO_LONGS(SECTION_BLOCKFLAGS_BITS) * sizeof(unsigned long);

-- 
2.43.0
Re: [PATCH v2 13/15] mm/sparse: move sparse_init_one_section() to internal.h
Posted by David Hildenbrand (Arm) 1 week, 4 days ago 
On 3/20/26 23:13, David Hildenbrand (Arm) wrote:
> While at it, convert the BUG_ON to a VM_WARN_ON_ONCE, avoid long lines, and
> merge sparse_encode_mem_map() into its only caller
> sparse_init_one_section().
> 
> Clarify the comment a bit, pointing at page_to_pfn().
> 
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
> ---
>  include/linux/mmzone.h |  2 +-
>  mm/internal.h          | 22 ++++++++++++++++++++++
>  mm/sparse.c            | 24 ------------------------
>  3 files changed, 23 insertions(+), 25 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index b694c69dee04..dcbbf36ed88c 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -2008,7 +2008,7 @@ struct mem_section {
>  	/*
>  	 * This is, logically, a pointer to an array of struct
>  	 * pages.  However, it is stored with some other magic.
> -	 * (see sparse.c::sparse_init_one_section())
> +	 * (see sparse_init_one_section())
>  	 *
>  	 * Additionally during early boot we encode node id of
>  	 * the location of the section here to guide allocation.
> diff --git a/mm/internal.h b/mm/internal.h
> index 5f5c45d80aca..2f188f7702f7 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -965,6 +965,28 @@ void memmap_init_range(unsigned long, int, unsigned long, unsigned long,
>   */
>  #ifdef CONFIG_SPARSEMEM
>  void sparse_init(void);
> +
> +static inline void sparse_init_one_section(struct mem_section *ms,
> +		unsigned long pnum, struct page *mem_map,
> +		struct mem_section_usage *usage, unsigned long flags)
> +{
> +	unsigned long coded_mem_map;
> +
> +	BUILD_BUG_ON(SECTION_MAP_LAST_BIT > PFN_SECTION_SHIFT);
> +
> +	/*
> +	 * We encode the start PFN of the section into the mem_map such that
> +	 * page_to_pfn() on !CONFIG_SPARSEMEM_VMEMMAP can simply subtract it
> +	 * from the page pointer to obtain the PFN.
> +	 */
> +	coded_mem_map = (unsigned long)(mem_map - section_nr_to_pfn(pnum));
> +	VM_WARN_ON(coded_mem_map & ~SECTION_MAP_MASK);
> +
> +	ms->section_mem_map &= ~SECTION_MAP_MASK;
> +	ms->section_mem_map |= coded_mem_map;
> +	ms->section_mem_map |= flags | SECTION_HAS_MEM_MAP;
> +	ms->usage = usage;

The following fixup on top:

From 66ec42c610feb3b84c405222f3f39ba0776549c6 Mon Sep 17 00:00:00 2001
From: "David Hildenbrand (Arm)" <david@kernel.org>
Date: Mon, 23 Mar 2026 09:48:21 +0100
Subject: [PATCH] fixup: mm/sparse: move sparse_init_one_section() to
 internal.h

Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
---
 mm/internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/internal.h b/mm/internal.h
index 2f188f7702f7..969e58e5b3db 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -980,7 +980,7 @@ static inline void sparse_init_one_section(struct mem_section *ms,
 	 * from the page pointer to obtain the PFN.
 	 */
 	coded_mem_map = (unsigned long)(mem_map - section_nr_to_pfn(pnum));
-	VM_WARN_ON(coded_mem_map & ~SECTION_MAP_MASK);
+	VM_WARN_ON_ONCE(coded_mem_map & ~SECTION_MAP_MASK);
 
 	ms->section_mem_map &= ~SECTION_MAP_MASK;
 	ms->section_mem_map |= coded_mem_map;
-- 
2.43.0


-- 
Cheers,

David

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