Re: [PATCH 5/5] mm: hugetlb: enable CMA allocation for PMD-sized pages

[Lance Yang]

On Fri, Oct 16, 2026 at 06:07:36PM +0800, Qi Zheng wrote:
>From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
[...]
>diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>index 218fbaee6f7e5..8c00fd9d0658d 100644
>--- a/mm/hugetlb.c
>+++ b/mm/hugetlb.c
>@@ -1362,18 +1362,8 @@ static struct folio *dequeue_hugetlb_folio(struct hstate *h, gfp_t gfp_mask,
> static struct folio *alloc_gigantic_frozen_folio(int order, gfp_t gfp_mask,
> 		int nid, nodemask_t *nodemask)
> {
>-	struct folio *folio;
>-
>-	folio = hugetlb_cma_alloc_frozen_folio(order, gfp_mask, nid, nodemask);
>-	if (folio)
>-		return folio;
>-
>-	if (hugetlb_cma_exclusive_alloc(order))
>-		return NULL;
>-
>-	folio = (struct folio *)alloc_contig_frozen_pages(1 << order, gfp_mask,
>-							  nid, nodemask);
>-	return folio;
>+	return (struct folio *)alloc_contig_frozen_pages(1 << order, gfp_mask,
>+							 nid, nodemask);
> }
> #else /* !CONFIG_ARCH_HAS_GIGANTIC_PAGE || !CONFIG_CONTIG_ALLOC */
> static struct folio *alloc_gigantic_frozen_folio(int order, gfp_t gfp_mask, int nid,
>@@ -1849,11 +1839,18 @@ static struct folio *only_alloc_fresh_hugetlb_folio(struct hstate *h,
> 	if (nid == NUMA_NO_NODE)
> 		nid = numa_mem_id();
> 
>-	if (order_is_gigantic(order))
>-		folio = alloc_gigantic_frozen_folio(order, gfp_mask, nid, nmask);
>-	else
>-		folio = alloc_buddy_frozen_folio(order, gfp_mask, nid, nmask,
>-						 node_alloc_noretry);
>+	folio = hugetlb_cma_alloc_frozen_folio(order, gfp_mask, nid, nmask);
>+	if (!folio) {

Emm ... what about PF_MEMALLOC_PIN here?

If a FOLL_LONGTERM migration out of CMA needs a fresh hugetlb folio,
this can allocate another CMA folio as the target.

With HVO disabled, the old folio is freed back to CMA and can be picked
again again again.

I guess we'd keep migrating between CMA folios without ever completing
the pin ... even if pinnable buddy memory is available, no?

[...]

Cheers, Lance