On Wed, 16 Sep 2026 14:43:30 +0800 Muchun Song <songmuchun@bytedance.com> wrote:
> This series is split out from the earlier, larger series "mm: Generalize
> HVO for HugeTLB and device DAX" [1]. While the parent series generalizes
> vmemmap optimization across HugeTLB and device DAX, this subset addresses
> a single, self-contained step: switching device DAX to the section-based
> sparse-vmemmap optimization infrastructure introduced for HugeTLB.
>
> 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 is intended to be the third smaller step toward the broader HVO
> generalization. The wider HVO consolidation between HugeTLB and device
> DAX is left for follow-up series.
Thanks, I updated mm-unstable to this version.
> v4:
> - Rename CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION to
> CONFIG_VMEMMAP_OPTIMIZATION (suggested by Mike Rapoport)
> - Collect Acked-by tags from Mike Rapoport
>
Here's how v4 altered mm.git:
arch/x86/entry/vdso/vdso32/fake_32bit_build.h | 2 +-
drivers/dax/Kconfig | 2 --
fs/Kconfig | 2 +-
include/linux/mm.h | 2 +-
include/linux/mmzone.h | 6 +++---
include/linux/page-flags.h | 2 +-
include/linux/vmemmap-optimization.h | 6 +++---
mm/Kconfig | 3 ++-
8 files changed, 12 insertions(+), 13 deletions(-)
--- a/arch/x86/entry/vdso/vdso32/fake_32bit_build.h~b
+++ a/arch/x86/entry/vdso/vdso32/fake_32bit_build.h
@@ -11,7 +11,7 @@
#undef CONFIG_PGTABLE_LEVELS
#undef CONFIG_ILLEGAL_POINTER_VALUE
#undef CONFIG_SPARSEMEM_VMEMMAP
-#undef CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION
+#undef CONFIG_VMEMMAP_OPTIMIZATION
#undef CONFIG_NR_CPUS
#undef CONFIG_PARAVIRT_XXL
--- a/drivers/dax/Kconfig~b
+++ a/drivers/dax/Kconfig
@@ -8,8 +8,6 @@ if DAX
config DEV_DAX
tristate "Device DAX: direct access mapping device"
depends on TRANSPARENT_HUGEPAGE
- depends on ZONE_DEVICE
- select SPARSEMEM_VMEMMAP_OPTIMIZATION if ARCH_WANT_OPTIMIZE_DAX_VMEMMAP
help
Support raw access to differentiated (persistence, bandwidth,
latency...) memory via an mmap(2) capable character
--- a/fs/Kconfig~b
+++ a/fs/Kconfig
@@ -278,7 +278,7 @@ config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
def_bool HUGETLB_PAGE
depends on ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
depends on SPARSEMEM_VMEMMAP
- select SPARSEMEM_VMEMMAP_OPTIMIZATION
+ select VMEMMAP_OPTIMIZATION
config HUGETLB_PMD_PAGE_TABLE_SHARING
def_bool HUGETLB_PAGE
--- a/include/linux/mm.h~b
+++ a/include/linux/mm.h
@@ -5174,7 +5174,7 @@ static inline bool __vmemmap_can_optimiz
unsigned long nr_pages;
unsigned long nr_vmemmap_pages;
- if (!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION))
+ if (!IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION))
return false;
if (!pgmap || !is_power_of_2(sizeof(struct page)))
--- a/include/linux/mmzone.h~b
+++ a/include/linux/mmzone.h
@@ -103,7 +103,7 @@
* HVO which is only active if the size of struct page is a power of 2.
*/
#define MAX_FOLIO_VMEMMAP_ALIGN \
- (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION) && \
+ (IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION) && \
is_power_of_2(sizeof(struct page)) ? \
MAX_FOLIO_NR_PAGES * sizeof(struct page) : 0)
@@ -117,7 +117,7 @@
(MAX_FOLIO_ORDER - VMEMMAP_OPTIMIZATION_MIN_ORDER + 1)
#define VMEMMAP_OPTIMIZATION_NR_ORDERS \
((__VMEMMAP_OPTIMIZATION_NR_ORDERS > 0 && \
- IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION)) ? __VMEMMAP_OPTIMIZATION_NR_ORDERS : 0)
+ IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION)) ? __VMEMMAP_OPTIMIZATION_NR_ORDERS : 0)
enum migratetype {
MIGRATE_UNMOVABLE,
@@ -2020,7 +2020,7 @@ struct mem_section {
unsigned long section_mem_map;
struct mem_section_usage *usage;
-#ifdef CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION
+#ifdef CONFIG_VMEMMAP_OPTIMIZATION
/*
* Normally, sections hold regular (order-0) pages. However, for
* sections with HVO enabled, this tracks the compound page order
--- a/include/linux/page-flags.h~b
+++ a/include/linux/page-flags.h
@@ -214,7 +214,7 @@ static __always_inline bool compound_inf
* but it requires validating that struct pages are naturally aligned
* for all orders up to the MAX_FOLIO_ORDER, which can be tricky.
*/
- if (!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION))
+ if (!IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION))
return false;
return is_power_of_2(sizeof(struct page));
--- a/include/linux/vmemmap-optimization.h~b
+++ a/include/linux/vmemmap-optimization.h
@@ -14,7 +14,7 @@
#include <linux/mmdebug.h>
#include <linux/mmzone.h>
-#ifdef CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION
+#ifdef CONFIG_VMEMMAP_OPTIMIZATION
static inline unsigned int section_compound_order(const struct mem_section *section)
{
return section->compound_page_order;
@@ -64,7 +64,7 @@ static inline unsigned int pfn_to_sectio
{
return 0;
}
-#endif /* CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION */
+#endif /* CONFIG_VMEMMAP_OPTIMIZATION */
static inline bool vmemmap_optimizable_pfn(unsigned long pfn)
{
@@ -79,7 +79,7 @@ static inline bool vmemmap_optimizable_p
static inline bool vmemmap_optimizable_order(unsigned int order)
{
- if (!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION))
+ if (!IS_ENABLED(CONFIG_VMEMMAP_OPTIMIZATION))
return false;
if (!is_power_of_2(sizeof(struct page)))
--- a/mm/Kconfig~b
+++ a/mm/Kconfig
@@ -461,7 +461,7 @@ config SPARSEMEM_VMEMMAP
pfn_to_page and page_to_pfn operations. This is the most
efficient option when sufficient kernel resources are available.
-config SPARSEMEM_VMEMMAP_OPTIMIZATION
+config VMEMMAP_OPTIMIZATION
bool
depends on SPARSEMEM_VMEMMAP
@@ -1224,6 +1224,7 @@ config ZONE_DMA32
config ZONE_DEVICE
bool "Device memory (pmem, HMM, etc...) hotplug support"
depends on MEMORY_HOTREMOVE
+ select VMEMMAP_OPTIMIZATION if ARCH_WANT_OPTIMIZE_DAX_VMEMMAP
select XARRAY_MULTI
help
_