Re: [PATCH RFC 2/3] mm: Add mempolicy support to the filemap layer

[Matthew Wilcox <willy@infradead.org>]

On Mon, Sep 16, 2024 at 04:57:42PM +0000, Shivank Garg wrote:
> @@ -652,6 +660,8 @@ static inline fgf_t fgf_set_order(size_t size)
>  void *filemap_get_entry(struct address_space *mapping, pgoff_t index);
>  struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>  		fgf_t fgp_flags, gfp_t gfp);
> +struct folio *__filemap_get_folio_mpol(struct address_space *mapping,
> +		pgoff_t index, fgf_t fgp_flags, gfp_t gfp, struct mempolicy *mpol);
>  struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
>  		fgf_t fgp_flags, gfp_t gfp);
>  
> @@ -710,6 +720,26 @@ static inline struct folio *filemap_grab_folio(struct address_space *mapping,
>  			mapping_gfp_mask(mapping));
>  }
>  
> +/**
> + * filemap_grab_folio_mpol - grab a folio from the page cache
> + * @mapping: The address space to search
> + * @index: The page index
> + * @mpol: The mempolicy to apply
> + *
> + * Same as filemap_grab_folio(), except that it allocates the folio using
> + * given memory policy.
> + *
> + * Return: A found or created folio. ERR_PTR(-ENOMEM) if no folio is found
> + * and failed to create a folio.
> + */
> +static inline struct folio *filemap_grab_folio_mpol(struct address_space *mapping,
> +					pgoff_t index, struct mempolicy *mpol)
> +{
> +	return __filemap_get_folio_mpol(mapping, index,
> +			FGP_LOCK | FGP_ACCESSED | FGP_CREAT,
> +			mapping_gfp_mask(mapping), mpol);
> +}

This should be conditional on CONFIG_NUMA, just like 
filemap_alloc_folio_mpol_noprof() above.

> @@ -1947,7 +1959,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>  			err = -ENOMEM;
>  			if (order > 0)
>  				alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;
> -			folio = filemap_alloc_folio(alloc_gfp, order);
> +			folio = filemap_alloc_folio_mpol_noprof(alloc_gfp, order, mpol);

Why use the _noprof variant here?

> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 9e9450433fcc..88da732cf2be 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2281,6 +2281,7 @@ struct folio *folio_alloc_mpol_noprof(gfp_t gfp, unsigned int order,
>  	return page_rmappable_folio(alloc_pages_mpol_noprof(gfp | __GFP_COMP,
>  							order, pol, ilx, nid));
>  }
> +EXPORT_SYMBOL(folio_alloc_mpol_noprof);

Why does this need to be exported?  What module will use it?