> On Aug 31, 2026, at 17:44, Qi Zheng <[email protected]> wrote:
>
>
>
> On 8/31/26 3:53 PM, Muchun Song wrote:
>> 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 <[email protected]>
>> ---
>> 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 <[email protected]>
Thanks.
>
> Thanks,
> Qi
>
> [1].
> https://sashiko.dev/#/patchset/20260831075342.57563-1-songmuchun%40bytedance.com
>
>> +
>> #
>> # 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)))
