On Sun, 27 Sep 2026 10:54:29 +0800 Muchun Song <[email protected]> wrote:
> After the HugeTLB conversion, optimized vmemmap state is described by
> the memory section and the sparse-vmemmap population path can allocate or
> reuse shared tail vmemmap pages based on that metadata. Device DAX still
> uses the older DAX-specific population model, including a separate tail
> vmemmap page reservation and architecture-specific logic to locate or
> populate reusable tail pages.
>
> This series makes device DAX use the same section-based model. Device DAX
> records the compound page order from pgmap->vmemmap_shift in section
> metadata before vmemmap population, uses the common per-zone shared tail
> vmemmap page, and drops the extra reserved tail page. The powerpc radix
> path is updated to use the same shared tail-page helper, so the generic
> and powerpc DAX paths follow the same reservation model.
Thanks, I've updated mm-unstable to this version.
Sashiko asked a thing:
https://sashiko.dev/#/patchset/[email protected]
> v5:
> - Move the shared tail-page factoring before introducing
> CONFIG_VMEMMAP_OPTIMIZATION
> - Add a new patch to allocate the per-zone shared tail-page array
> dynamically and fix the RISC-V build failure reported by the kernel
> test robot
> - Select VMEMMAP_OPTIMIZATION from ZONE_DEVICE instead of DEV_DAX so
> MSHV_VTL cannot set vmemmap_shift while leaving the optimization
> disabled (reported by Sashiko)
> - Move the vmemmap optimization macros and MAX_FOLIO_VMEMMAP_ALIGN from
> mmzone.h to vmemmap-optimization.h
Here's how v5 altered mm.git:
arch/loongarch/include/asm/pgtable.h | 1
arch/riscv/mm/init.c | 1
include/linux/mm.h | 1
include/linux/mmzone.h | 27 +----------------
include/linux/vmemmap-optimization.h | 29 ++++++++++++++++--
mm/hugetlb_vmemmap.c | 1
mm/sparse-vmemmap.c | 39 +++++++++++++++++++++----
7 files changed, 64 insertions(+), 35 deletions(-)
--- a/arch/loongarch/include/asm/pgtable.h~b
+++ a/arch/loongarch/include/asm/pgtable.h
@@ -72,6 +72,7 @@
#include <linux/mm_types.h>
#include <linux/mmzone.h>
+#include <linux/vmemmap-optimization.h>
#include <asm/fixmap.h>
#include <asm/sparsemem.h>
--- a/arch/riscv/mm/init.c~b
+++ a/arch/riscv/mm/init.c
@@ -22,6 +22,7 @@
#include <linux/hugetlb.h>
#include <linux/kfence.h>
#include <linux/execmem.h>
+#include <linux/vmemmap-optimization.h>
#include <asm/alternative.h>
#include <asm/fixmap.h>
--- a/include/linux/mm.h~b
+++ a/include/linux/mm.h
@@ -38,6 +38,7 @@
#include <linux/bitops.h>
#include <linux/iommu-debug-pagealloc.h>
#include <linux/kcsan-checks.h>
+#include <linux/vmemmap-optimization.h>
struct mempolicy;
struct anon_vma;
--- a/include/linux/mmzone.h~b
+++ a/include/linux/mmzone.h
@@ -96,29 +96,6 @@
#define MAX_FOLIO_NR_PAGES (1UL << MAX_FOLIO_ORDER)
-/*
- * HugeTLB Vmemmap Optimization (HVO) requires struct pages of the head page to
- * be naturally aligned with regard to the folio size.
- *
- * HVO which is only active if the size of struct page is a power of 2.
- */
-#define MAX_FOLIO_VMEMMAP_ALIGN \
- (IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION) && \
- is_power_of_2(sizeof(struct page)) ? \
- MAX_FOLIO_NR_PAGES * sizeof(struct page) : 0)
-
-/* The number of retained vmemmap pages with HVO enabled. */
-#define VMEMMAP_OPTIMIZATION_PAGES 1
-#define VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES \
- (VMEMMAP_OPTIMIZATION_PAGES * PAGE_SIZE / sizeof(struct page))
-#define VMEMMAP_OPTIMIZATION_MIN_ORDER
(ilog2(VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES) + 1)
-
-#define __VMEMMAP_OPTIMIZATION_NR_ORDERS \
- (MAX_FOLIO_ORDER - VMEMMAP_OPTIMIZATION_MIN_ORDER + 1)
-#define VMEMMAP_OPTIMIZATION_NR_ORDERS \
- ((__VMEMMAP_OPTIMIZATION_NR_ORDERS > 0 && \
- IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION)) ?
__VMEMMAP_OPTIMIZATION_NR_ORDERS : 0)
-
enum migratetype {
MIGRATE_UNMOVABLE,
MIGRATE_MOVABLE,
@@ -1156,8 +1133,8 @@ struct zone {
/* Zone statistics */
atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];
atomic_long_t vm_numa_event[NR_VM_NUMA_EVENT_ITEMS];
-#ifdef CONFIG_SPARSEMEM_VMEMMAP
- struct page *vmemmap_tails[VMEMMAP_OPTIMIZATION_NR_ORDERS];
+#ifdef CONFIG_VMEMMAP_OPTIMIZATION
+ struct page **vmemmap_tails;
#endif
} ____cacheline_internodealigned_in_smp;
--- a/include/linux/vmemmap-optimization.h~b
+++ a/include/linux/vmemmap-optimization.h
@@ -14,6 +14,23 @@
#include <linux/mmdebug.h>
#include <linux/mmzone.h>
+/*
+ * HugeTLB Vmemmap Optimization (HVO) requires struct pages of the head page to
+ * be naturally aligned with regard to the folio size.
+ *
+ * HVO which is only active if the size of struct page is a power of 2.
+ */
+#define MAX_FOLIO_VMEMMAP_ALIGN \
+ (IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION) && \
+ is_power_of_2(sizeof(struct page)) ? \
+ MAX_FOLIO_NR_PAGES * sizeof(struct page) : 0)
+
+/* The number of retained vmemmap pages with HVO enabled. */
+#define VMEMMAP_OPTIMIZATION_PAGES 1
+#define VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES \
+ (VMEMMAP_OPTIMIZATION_PAGES * PAGE_SIZE / sizeof(struct page))
+#define VMEMMAP_OPTIMIZATION_MIN_ORDER
(ilog2(VMEMMAP_OPTIMIZATION_NR_STRUCT_PAGES) + 1)
+
#ifdef CONFIG_VMEMMAP_OPTIMIZATION
static inline unsigned int section_compound_order(const struct mem_section
*section)
{
@@ -44,6 +61,8 @@ static inline unsigned int pfn_to_sectio
{
return section_compound_order(__pfn_to_section(pfn));
}
+
+struct page *vmemmap_shared_tail_page(unsigned int order, struct zone *zone);
#else
static inline unsigned int section_compound_order(const struct mem_section
*section)
{
@@ -64,6 +83,12 @@ static inline unsigned int pfn_to_sectio
{
return 0;
}
+
+static inline struct page *vmemmap_shared_tail_page(unsigned int order,
+ struct zone *zone)
+{
+ return NULL;
+}
#endif /* CONFIG_VMEMMAP_OPTIMIZATION */
static inline bool vmemmap_optimizable_pfn(unsigned long pfn)
@@ -87,8 +112,4 @@ static inline bool vmemmap_optimizable_o
return order >= VMEMMAP_OPTIMIZATION_MIN_ORDER;
}
-
-#ifdef CONFIG_SPARSEMEM_VMEMMAP
-struct page *vmemmap_shared_tail_page(unsigned int order, struct zone *zone);
-#endif /* CONFIG_SPARSEMEM_VMEMMAP */
#endif /* _LINUX_VMEMMAP_OPTIMIZATION_H */
--- a/mm/hugetlb_vmemmap.c~b
+++ a/mm/hugetlb_vmemmap.c
@@ -19,7 +19,6 @@
#include <asm/tlbflush.h>
#include "hugetlb_vmemmap.h"
-#include "internal.h"
/**
* struct vmemmap_remap_walk - walk vmemmap page table
--- a/mm/sparse-vmemmap.c~b
+++ a/mm/sparse-vmemmap.c
@@ -167,16 +167,44 @@ static void * __meminit vmemmap_alloc_bl
return p;
}
+#ifdef CONFIG_VMEMMAP_OPTIMIZATION
+#define VMEMMAP_OPTIMIZATION_NR_ORDERS (MAX_FOLIO_ORDER -
VMEMMAP_OPTIMIZATION_MIN_ORDER + 1)
+
+static __ref struct page **vmemmap_tails_alloc(struct zone *zone)
+{
+ struct page **pages;
+ const size_t size = array_size(VMEMMAP_OPTIMIZATION_NR_ORDERS,
sizeof(*pages));
+
+ pages = slab_is_available() ? kzalloc_objs(*pages,
VMEMMAP_OPTIMIZATION_NR_ORDERS) :
+ memblock_alloc(size, __alignof__(*pages));
+ if (!pages)
+ return NULL;
+
+ if (cmpxchg(&zone->vmemmap_tails, NULL, pages) != NULL) {
+ if (slab_is_available())
+ kfree(pages);
+ else
+ memblock_free(pages, size);
+ pages = READ_ONCE(zone->vmemmap_tails);
+ }
+
+ return pages;
+}
+
struct page __ref *vmemmap_shared_tail_page(unsigned int order, struct zone
*zone)
{
void *addr;
- struct page *page;
+ struct page *page, **pages;
const unsigned int idx = order - VMEMMAP_OPTIMIZATION_MIN_ORDER;
- if (WARN_ON_ONCE(idx >= ARRAY_SIZE(zone->vmemmap_tails)))
+ if (WARN_ON_ONCE(idx >= VMEMMAP_OPTIMIZATION_NR_ORDERS))
+ return NULL;
+
+ pages = READ_ONCE(zone->vmemmap_tails) ? : vmemmap_tails_alloc(zone);
+ if (!pages)
return NULL;
- page = READ_ONCE(zone->vmemmap_tails[idx]);
+ page = READ_ONCE(pages[idx]);
if (likely(page))
return page;
@@ -196,16 +224,17 @@ struct page __ref *vmemmap_shared_tail_p
}
page = virt_to_page(addr);
- if (cmpxchg(&zone->vmemmap_tails[idx], NULL, page) != NULL) {
+ if (cmpxchg(&pages[idx], NULL, page) != NULL) {
if (slab_is_available())
__free_page(page);
else
memblock_free(addr, PAGE_SIZE);
- page = READ_ONCE(zone->vmemmap_tails[idx]);
+ page = READ_ONCE(pages[idx]);
}
return page;
}
+#endif
static __meminit void *vmemmap_alloc_pte(unsigned long pfn, int node,
struct vmem_altmap *altmap, unsigned long flags)
_
