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

On Aug 31, 2026, at 17:44, Qi Zheng [off-list ref] wrote:



On 8/31/26 3:53 PM, Muchun Song wrote:

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
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>
---
 arch/x86/entry/vdso/vdso32/fake_32bit_build.h |  2 +-
 drivers/dax/Kconfig                           |  1 +
 fs/Kconfig                                    |  1 +
 include/linux/mm.h                            |  3 +++
 include/linux/mmzone.h                        | 13 +++++++------
 include/linux/page-flags.h                    |  5 ++---
 mm/Kconfig                                    |  3 +++
 mm/sparse.h                                   |  4 ++--
 8 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/arch/x86/entry/vdso/vdso32/fake_32bit_build.h b/arch/x86/entry/vdso/vdso32/fake_32bit_build.h
index bc3e549795c3..5f8424eade2b 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 602f9a0839a9..85ad4c135cdd 100644
--- a/drivers/dax/Kconfig
+++ b/drivers/dax/Kconfig

@@ -8,6 +8,7 @@ if DAX
 config DEV_DAX
  tristate "Device DAX: direct access mapping device"
  depends on TRANSPARENT_HUGEPAGE
+ 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 d1c210c6508f..9b32ce79cc80 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 a9fbe26536f4..edadd7549b72 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -5188,6 +5188,9 @@ 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 c9ae7991a8b2..e9b54ea0eff0 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 ae2ebaed6d4d..de3c06062bc6 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 c1ddf59c0d71..b5f8372cd164 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig

@@ -461,6 +461,9 @@ 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

As sashiko was concerned about [1], it seems we need to add

       depends on SPARSEMEM_VMEMMAP

here.

You are right. Besides that, we also need DEV_DAX to depend on
ZONE_DEVICE explicitly.

Apart from that, LGTM. With this fix included:

Acked-by: Qi Zheng <qi.zheng@linux.dev>

Thanks.

Thanks,
Qi

[1]. https://sashiko.dev/#/patchset/20260831075342.57563-1-songmuchun%40bytedance.com

quoted

+
 #
 # 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 049272aba84e..b408d15baf7b 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_order(const struct mem_section *section)
 {
  	return section->order;

@@ -72,7 +72,7 @@ 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)))