[PATCH v5 08/17] mm/sparse-vmemmap: support section-based vmemmap optimization
From: Muchun Song
Date: Tue Aug 25 2026 - 04:52:26 EST
Teach sparse-vmemmap population code to use the compound page order
when deciding whether a vmemmap page can be optimized.
With this information, the common sparse-vmemmap population path can
allocate or reuse shared tail vmemmap pages directly instead of relying
on HugeTLB-specific handling.
This centralizes vmemmap optimization logic in the sparse-vmemmap code,
based on section metadata, and prepares for sharing the same mechanism
across different users of vmemmap optimization, including HugeTLB and
DAX.
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
v5:
- Add vmemmap_alloc_pte() to keep PTE allocation handling clearer
(suggested by Mike Rapoport)
- Move preparatory section_nr_vmemmap_pages() changes to the previous
patch (suggested by Mike Rapoport)
v4:
- Move section_nr_vmemmap_pages() outside CONFIG_MEMORY_HOTPLUG to
fix CONFIG_MEMORY_HOTPLUG=n builds (reported by kernel test robot)
v2:
- Keep vmemmap accounting and population logic in sparse-vmemmap.c
(suggested by Mike Rapoport)
- Move vmemmap_get_tail() before its first use instead of adding only a
forward declaration in the previous patch (suggested by Mike Rapoport)
- Simplify the PMD path handling for HVO-covered sections
---
mm/sparse-vmemmap.c | 46 +++++++++++++++++++++++++++++++++++++--------
mm/sparse.c | 4 ++--
mm/sparse.h | 7 +++++++
3 files changed, 47 insertions(+), 10 deletions(-)
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index ea3cacec0a79..8d39196f6d93 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -148,8 +148,7 @@ void __meminit vmemmap_verify(pte_t *pte, int node,
start, end - 1);
}
-#ifdef CONFIG_MEMORY_HOTPLUG
-static int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,
+int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,
struct vmem_altmap *altmap, struct dev_pagemap *pgmap)
{
const struct mem_section *ms = __pfn_to_section(pfn);
@@ -175,7 +174,6 @@ static int __meminit section_nr_vmemmap_pages(unsigned long pfn, unsigned long n
return 0;
}
-#endif
static void * __meminit vmemmap_alloc_block_zero(unsigned long size, int node)
{
@@ -215,19 +213,44 @@ static __meminit struct page *vmemmap_get_tail(unsigned int order, struct zone *
return tail;
}
+#else
+static inline struct page *vmemmap_get_tail(unsigned int order, struct zone *zone)
+{
+ return NULL;
+}
#endif
+static __meminit void *vmemmap_alloc_pte(unsigned long pfn, int node,
+ struct vmem_altmap *altmap)
+{
+ struct zone *zone;
+ struct page *page;
+ const unsigned int order = pfn_to_section_order(pfn);
+
+ if (!vmemmap_optimizable_pfn(pfn))
+ return vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
+
+ zone = pfn_to_zone(pfn, node);
+ page = vmemmap_get_tail(order, zone);
+ if (!page)
+ return NULL;
+
+ return page_address(page);
+}
+
static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node,
struct vmem_altmap *altmap,
unsigned long ptpfn, unsigned long flags)
{
pte_t *pte = pte_offset_kernel(pmd, addr);
+ unsigned long pfn = page_to_pfn((struct page *)addr);
+
if (pte_none(ptep_get(pte))) {
pte_t entry;
- void *p;
if (ptpfn == (unsigned long)-1) {
- p = vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
+ void *p = vmemmap_alloc_pte(pfn, node, altmap);
+
if (!p)
return NULL;
ptpfn = PHYS_PFN(__pa(p));
@@ -246,7 +269,8 @@ static pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, in
}
entry = pfn_pte(ptpfn, PAGE_KERNEL);
set_pte_at(&init_mm, addr, pte, entry);
- }
+ } else if (WARN_ON_ONCE(vmemmap_optimizable_pfn(pfn)))
+ return NULL;
return pte;
}
@@ -435,6 +459,9 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
pmd_t *pmd;
for (addr = start; addr < end; addr = next) {
+ unsigned long pfn = page_to_pfn((struct page *)addr);
+ const struct mem_section *ms = __pfn_to_section(pfn);
+
next = pmd_addr_end(addr, end);
pgd = vmemmap_pgd_populate(addr, node);
@@ -450,7 +477,7 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
return -ENOMEM;
pmd = pmd_offset(pud, addr);
- if (pmd_none(pmdp_get(pmd))) {
+ if (pmd_none(pmdp_get(pmd)) && !section_vmemmap_optimizable(ms)) {
void *p;
p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
@@ -468,8 +495,11 @@ int __meminit vmemmap_populate_hugepages(unsigned long start, unsigned long end,
*/
return -ENOMEM;
}
- } else if (vmemmap_check_pmd(pmd, node, addr, next))
+ } else if (vmemmap_check_pmd(pmd, node, addr, next)) {
+ if (WARN_ON_ONCE(section_vmemmap_optimizable(ms)))
+ return -EOPNOTSUPP;
continue;
+ }
if (vmemmap_populate_basepages(addr, next, node, altmap))
return -ENOMEM;
}
diff --git a/mm/sparse.c b/mm/sparse.c
index c84b4c7b8c70..e6cb67ca9c8d 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -305,8 +305,8 @@ static void __init sparse_init_nid(int nid, unsigned long pnum_begin,
nid, NULL, NULL);
if (!map)
panic("Failed to allocate memmap for section %lu\n", pnum);
- memmap_boot_pages_add(DIV_ROUND_UP(PAGES_PER_SECTION * sizeof(struct page),
- PAGE_SIZE));
+ memmap_boot_pages_add(section_nr_vmemmap_pages(pfn, PAGES_PER_SECTION,
+ NULL, NULL));
sparse_init_early_section(nid, map, pnum, 0);
}
}
diff --git a/mm/sparse.h b/mm/sparse.h
index 02ed0f34eac8..e427d72e9c2d 100644
--- a/mm/sparse.h
+++ b/mm/sparse.h
@@ -111,8 +111,15 @@ static inline void sparse_init(void) {}
*/
#ifdef CONFIG_SPARSEMEM_VMEMMAP
void sparse_init_subsection_map(void);
+int section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,
+ struct vmem_altmap *altmap, struct dev_pagemap *pgmap);
#else
static inline void sparse_init_subsection_map(void) {}
+static inline int section_nr_vmemmap_pages(unsigned long pfn, unsigned long nr_pages,
+ struct vmem_altmap *altmap, struct dev_pagemap *pgmap)
+{
+ return DIV_ROUND_UP(nr_pages * sizeof(struct page), PAGE_SIZE);
+}
#endif /* CONFIG_SPARSEMEM_VMEMMAP */
#endif /* __MM_SPARSE_H */
--
2.54.0