Re: [PATCHv2 2/3] x86/64/mm: Make SPARSEMEM_VMEMMAP the only memory model

[Ard Biesheuvel]

On Fri, 16 May 2025 at 10:15, Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>
> 5-level paging only supports SPARSEMEM_VMEMMAP. CONFIG_X86_5LEVEL is
> being phased out, making 5-level paging support mandatory.
>
> Make CONFIG_SPARSEMEM_VMEMMAP mandatory for x86-64 and eliminate
> any associated conditional statements.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>

> ---
>  arch/x86/Kconfig      | 2 +-
>  arch/x86/mm/init_64.c | 9 +--------
>  2 files changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index d3c2da3b2f0b..45b36a019b5e 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1467,7 +1467,6 @@ config X86_PAE
>  config X86_5LEVEL
>         bool "Enable 5-level page tables support"
>         default y
> -       select SPARSEMEM_VMEMMAP
>         depends on X86_64
>         help
>           5-level paging enables access to larger address space:
> @@ -1579,6 +1578,7 @@ config ARCH_SPARSEMEM_ENABLE
>         def_bool y
>         select SPARSEMEM_STATIC if X86_32
>         select SPARSEMEM_VMEMMAP_ENABLE if X86_64
> +       select SPARSEMEM_VMEMMAP if X86_64
>
>  config ARCH_SPARSEMEM_DEFAULT
>         def_bool X86_64 || (NUMA && X86_32)
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index bf45c7aed336..66330fe4e18c 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -833,7 +833,6 @@ void __init paging_init(void)
>         zone_sizes_init();
>  }
>
> -#ifdef CONFIG_SPARSEMEM_VMEMMAP
>  #define PAGE_UNUSED 0xFD
>
>  /*
> @@ -932,7 +931,6 @@ static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned long
>         if (!IS_ALIGNED(end, PMD_SIZE))
>                 unused_pmd_start = end;
>  }
> -#endif
>
>  /*
>   * Memory hotplug specific functions
> @@ -1152,16 +1150,13 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end,
>                                 pmd_clear(pmd);
>                                 spin_unlock(&init_mm.page_table_lock);
>                                 pages++;
> -                       }
> -#ifdef CONFIG_SPARSEMEM_VMEMMAP
> -                       else if (vmemmap_pmd_is_unused(addr, next)) {
> +                       } else if (vmemmap_pmd_is_unused(addr, next)) {
>                                         free_hugepage_table(pmd_page(*pmd),
>                                                             altmap);
>                                         spin_lock(&init_mm.page_table_lock);
>                                         pmd_clear(pmd);
>                                         spin_unlock(&init_mm.page_table_lock);
>                         }
> -#endif
>                         continue;
>                 }
>
> @@ -1500,7 +1495,6 @@ unsigned long memory_block_size_bytes(void)
>         return memory_block_size_probed;
>  }
>
> -#ifdef CONFIG_SPARSEMEM_VMEMMAP
>  /*
>   * Initialise the sparsemem vmemmap using huge-pages at the PMD level.
>   */
> @@ -1647,4 +1641,3 @@ void __meminit vmemmap_populate_print_last(void)
>                 node_start = 0;
>         }
>  }
> -#endif
> --
> 2.47.2
>