On 3/9/21 1:40 PM, Oscar Salvador wrote:
> +static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned 
> long end)
> +{
> +     /*
> +      * Could be our memmap page is filled with PAGE_UNUSED already from a
> +      * previous remove. Make sure to reset it.
> +      */
> +     vmemmap_use_sub_pmd(start);
> +
> +     /*
> +      * Mark with PAGE_UNUSED the unused parts of the new memmap range
> +      */
> +     if (!IS_ALIGNED(start, PMD_SIZE))
> +             memset((void *)start, PAGE_UNUSED,
> +                     start - ALIGN_DOWN(start, PMD_SIZE));
> +     if (!IS_ALIGNED(end, PMD_SIZE))
> +             memset((void *)end, PAGE_UNUSED,
> +                     ALIGN(end, PMD_SIZE) - end);
> +}
> +#endif

This is apparently under both CONFIG_SPARSEMEM_VMEMMAP and
CONFIG_MEMORY_HOTPLUG #ifdefs.  It errors out at compile-time with this
config: https://sr71.net/~dave/intel/config-mmotm-20210311

> linux.git/arch/x86/mm/init_64.c: In function 'vmemmap_populate_hugepages':
> linux.git/arch/x86/mm/init_64.c:1585:6: error: implicit declaration of 
> function 'vmemmap_use_new_sub_pmd' [-Werror=implicit-function-declaration]
>       vmemmap_use_new_sub_pmd(addr, next);
>       ^~~~~~~~~~~~~~~~~~~~~~~
> /home/davehans/linux.git/arch/x86/mm/init_64.c:1591:4: error: implicit 
> declaration of function 'vmemmap_use_sub_pmd' 
> [-Werror=implicit-function-declaration]
>     vmemmap_use_sub_pmd(addr, next);
>     ^~~~~~~~~~~~~~~~~~~

I didn't see a quick fix other than #ifdef'ing the call sites, which is
pretty ugly.

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