[PATCH 12/14] mm/sparse: move sparse_init_one_section() to internal.h

David Hildenbrand (Arm)
2026-03-17T16:57:54Z

While at it, convert the BUG_ON to a WARN_ON, avoid long lines, and merge
sparse_encode_mem_map() into sparse_init_one_section().

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

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..bcf4df97b185 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 |= SECTION_HAS_MEM_MAP | flags;
+ ms->usage = usage;
+}
#else
static inline void sparse_init(void) {}
#endif /* CONFIG_SPARSEMEM */
diff --git a/mm/sparse.c b/mm/sparse.c
index b5a2de43ac40..6f5f340301a3 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