Re: [PATCH v2 3/6] mm: hugetlb: Move mpol interpretation out of dequeue_hugetlb_folio_vma()

[Oscar Salvador <osalvador@suse.de>]

On Wed, May 06, 2026 at 08:54:39AM -0700, Ackerley Tng via B4 Relay wrote:
> From: Ackerley Tng <ackerleytng@google.com>
> 
> Move memory policy interpretation out of dequeue_hugetlb_folio_vma() and
> into alloc_hugetlb_folio() to separate reading and interpretation of memory
> policy from actual allocation.
> 
> Also rename dequeue_hugetlb_folio_vma() to
> dequeue_hugetlb_folio_with_mpol() to remove association with vma and to
> align with alloc_buddy_hugetlb_folio_with_mpol().
> 
> This will later allow memory policy to be interpreted outside of the
> process of allocating a hugetlb folio entirely. This opens doors for other
> callers of the HugeTLB folio allocation function, such as guest_memfd,
> where memory may not always be mapped and hence may not have an associated
> vma.
> 
> No functional change intended.
> 
> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
> Reviewed-by: James Houghton <jthoughton@google.com>
> ---
>  mm/hugetlb.c | 34 +++++++++++++++-------------------
>  1 file changed, 15 insertions(+), 19 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index ea3bc405b3162..3395de4d0999a 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1334,18 +1334,11 @@ static unsigned long available_huge_pages(struct hstate *h)
>  	return h->free_huge_pages - h->resv_huge_pages;
>  }
>  
> -static struct folio *dequeue_hugetlb_folio_vma(struct hstate *h,
> -				struct vm_area_struct *vma,
> -				unsigned long address)
> +static struct folio *dequeue_hugetlb_folio_with_mpol(struct hstate *h,
> +		struct mempolicy *mpol, int nid, nodemask_t *nodemask)
>  {
>  	struct folio *folio = NULL;
> -	struct mempolicy *mpol;
> -	gfp_t gfp_mask;
> -	nodemask_t *nodemask;
> -	int nid;
> -
> -	gfp_mask = htlb_alloc_mask(h);
> -	nid = huge_node(vma, address, gfp_mask, &mpol, &nodemask);
> +	gfp_t gfp_mask = htlb_alloc_mask(h);

Same thing here, you already have the mask from the caller.

> @@ -2866,6 +2858,9 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
>  	int ret, idx;
>  	struct hugetlb_cgroup *h_cg = NULL;
>  	gfp_t gfp = htlb_alloc_mask(h);
> +	struct mempolicy *mpol;
> +	nodemask_t *nodemask;
> +	int nid;
>  
>  	idx = hstate_index(h);
>  
> @@ -2926,6 +2921,9 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
>  
>  	spin_lock_irq(&hugetlb_lock);
>  
> +	/* Takes reference on mpol. */
> +	nid = huge_node(vma, addr, gfp, &mpol, &nodemask);

I know that before the refactoring we called huge_node() with the lock
taken, but I think that was just because dequeue_hugetlb_folio_vma()
needed that.
Now, I think we can just have it out of the lock.

Bottom line is we should really make crystal clear what needs to go with
or without the lock, because we have some history in hugetlb land about
know fully knowning what protects what and why.

If you think we still need to call it under the lock, I would state why,
but I do not think we do.

 

-- 
Oscar Salvador
SUSE Labs