Re: [PATCH RFC v3 03/35] mm: page_alloc: Add an arch hook to filter MIGRATE_CMA allocations

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 1/25/24 22:12, Alexandru Elisei wrote:
> As an architecture might have specific requirements around the allocation
> of CMA pages, add an arch hook that can disable allocations from
> MIGRATE_CMA, if the allocation was otherwise allowed.
> 
> This will be used by arm64, which will put tag storage pages on the
> MIGRATE_CMA list, and tag storage pages cannot be tagged. The filter will
> be used to deny using MIGRATE_CMA for __GFP_TAGGED allocations.

Just wondering how allocation requests would be blocked for direct
alloc_contig_range() requests ?

> 
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
>  include/linux/pgtable.h | 7 +++++++
>  mm/page_alloc.c         | 3 ++-
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 6d98d5fdd697..c5ddec6b5305 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -905,6 +905,13 @@ static inline void arch_do_swap_page(struct mm_struct *mm,
>  static inline void arch_free_pages_prepare(struct page *page, int order) { }
>  #endif
>  
> +#ifndef __HAVE_ARCH_ALLOC_CMA

Same as last patch i.e __HAVE_ARCH_ALLOC_CMA could be avoided via
a direct check on #ifndef arch_alloc_cma instead.

> +static inline bool arch_alloc_cma(gfp_t gfp)
> +{
> +	return true;
> +}
> +#endif
> +
>  #ifndef __HAVE_ARCH_UNMAP_ONE
>  /*
>   * Some architectures support metadata associated with a page. When a
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 27282a1c82fe..a96d47a6393e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3157,7 +3157,8 @@ static inline unsigned int gfp_to_alloc_flags_cma(gfp_t gfp_mask,
>  						  unsigned int alloc_flags)
>  {
>  #ifdef CONFIG_CMA
> -	if (gfp_migratetype(gfp_mask) == MIGRATE_MOVABLE)
> +	if (gfp_migratetype(gfp_mask) == MIGRATE_MOVABLE &&
> +	    arch_alloc_cma(gfp_mask))
>  		alloc_flags |= ALLOC_CMA;
>  #endif
>  	return alloc_flags;