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

[Muchun Song <muchun.song@linux.dev>]

> On Sep 14, 2026, at 15:48, Mike Rapoport <rppt@kernel.org> wrote:
> 
> Hi,

Hi,

> 
>> 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.

> 
>> 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 <songmuchun@bytedance.com>
>> 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.
>