Re: [PATCH v3 01/11] mm/sparse-vmemmap: introduce CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION

On Sep 14, 2026, at 15:48, Mike Rapoport [off-list ref] wrote:

Hi,

Hi,

quoted

The section-based vmemmap optimization infrastructure is still guarded by
CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP, but it also can be used by device
DAX. Introduce CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION as a common config

CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION is a bit mouthful :)

I think that dropping _SPARSEMEM won't hurt readability.

Yes, I'll simplify it in v4.

quoted

for the shared infrastructure.

Select the new option from HUGETLB_PAGE_OPTIMIZE_VMEMMAP and from
DEV_DAX when the architecture opts in to DAX vmemmap optimization, and
use it to guard the generic sparse-vmemmap state and helpers.

Signed-off-by: Muchun Song <redacted>
Acked-by: Qi Zheng <qi.zheng@linux.dev>

diff --git a/arch/x86/entry/vdso/vdso32/fake_32bit_build.h b/arch/x86/entry/vdso/vdso32/fake_32bit_build.h
index bc3e549795c3f..5f8424eade2bd 100644
--- a/arch/x86/entry/vdso/vdso32/fake_32bit_build.h
+++ b/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_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+#undef CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION
#undef CONFIG_NR_CPUS
#undef CONFIG_PARAVIRT_XXL

diff --git a/drivers/dax/Kconfig b/drivers/dax/Kconfig
index 602f9a0839a91..6250954b0fa7a 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig

@@ -8,6 +8,8 @@ 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

diff --git a/fs/Kconfig b/fs/Kconfig
index d1c210c6508f0..9b32ce79cc805 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig

@@ -278,6 +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

config HUGETLB_PMD_PAGE_TABLE_SHARING
def_bool HUGETLB_PAGE

diff --git a/include/linux/mm.h b/include/linux/mm.h
index c49ef99b4413b..a2ebe87e76546 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -5175,6 +5175,9 @@ static inline bool __vmemmap_can_optimize(struct vmem_altmap *altmap,

unsigned long nr_pages;
unsigned long nr_vmemmap_pages;

+ if (!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION))
+ return false;
+
if (!pgmap || !is_power_of_2(sizeof(struct page)))
return false;

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index acd94cecc0d39..97511f651ebc0 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h

@@ -102,9 +102,9 @@
 *
 * HVO which is only active if the size of struct page is a power of 2.
 */
-#define MAX_FOLIO_VMEMMAP_ALIGN \
- (IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP) && \
- is_power_of_2(sizeof(struct page)) ? \
+#define MAX_FOLIO_VMEMMAP_ALIGN \
+ (IS_ENABLED(CONFIG_SPARSEMEM_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. */

@@ -116,7 +116,8 @@

#define __VMEMMAP_OPTIMIZATION_NR_ORDERS \
(MAX_FOLIO_ORDER - VMEMMAP_OPTIMIZATION_MIN_ORDER + 1)
#define VMEMMAP_OPTIMIZATION_NR_ORDERS \
- (__VMEMMAP_OPTIMIZATION_NR_ORDERS > 0 ? __VMEMMAP_OPTIMIZATION_NR_ORDERS : 0)
+ ((__VMEMMAP_OPTIMIZATION_NR_ORDERS > 0 && \
+  IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION)) ? __VMEMMAP_OPTIMIZATION_NR_ORDERS : 0)

enum migratetype {
MIGRATE_UNMOVABLE,

@@ -1155,7 +1156,7 @@ 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_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+#ifdef CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION
struct page *vmemmap_tails[VMEMMAP_OPTIMIZATION_NR_ORDERS];
#endif
} ____cacheline_internodealigned_in_smp;

@@ -2019,7 +2020,7 @@ struct mem_section {

unsigned long section_mem_map;

struct mem_section_usage *usage;
-#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+#ifdef CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION
/*
* Normally, sections hold regular (order-0) pages. However, for
* sections with HVO enabled, this tracks the compound page order

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 86dd0470da117..462e89e055485 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h

@@ -208,14 +208,13 @@ enum pageflags {

static __always_inline bool compound_info_has_mask(void)
{
/*
- * Limit mask usage to HugeTLB vmemmap optimization (HVO) where it
- * makes a difference.
+ * Limit mask usage to HVO where it makes a difference.
*
* The approach with mask would work in the wider set of conditions,
* 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_HUGETLB_PAGE_OPTIMIZE_VMEMMAP))
+ if (!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION))
return false;

return is_power_of_2(sizeof(struct page));

diff --git a/mm/Kconfig b/mm/Kconfig
index bc7befafb47b5..c180d40cd6712 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig

@@ -461,6 +461,10 @@ 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
+ bool
+ depends on SPARSEMEM_VMEMMAP
+

#
# Select this config option from the architecture Kconfig, if it is preferred
# to enable the feature of HugeTLB/dev_dax vmemmap optimization.

diff --git a/mm/sparse.h b/mm/sparse.h
index d3a71ef4fad0f..3151d4db75753 100644
--- a/mm/sparse.h
+++ b/mm/sparse.h

@@ -10,7 +10,7 @@

#include <linux/mmzone.h>

-#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+#ifdef CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION
static inline unsigned int section_compound_order(const struct mem_section *section)
{
return section->compound_page_order;

@@ -75,7 +75,7 @@ static inline bool vmemmap_optimizable_pfn(unsigned long pfn)

static inline bool vmemmap_optimizable_order(unsigned int order)
{
- if (!IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP))
+ if (!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP_OPTIMIZATION))
return false;

if (!is_power_of_2(sizeof(struct page)))

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Thank you Mike.

-- 
Sincerely yours,
Mike.