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

[Qi Zheng <qi.zheng@linux.dev>]

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

Apart from that, LGTM. With this fix included:

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

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)))