Re: [PATCH v4 3/3] mm: hugetlb: fix GFP mask propagation to CMA

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 11/11/2026 2:46 PM, Qi Zheng wrote:
> From: Qi Zheng <zhengqi.arch@bytedance.com>
> 
> cma_alloc_frozen_compound() uses GFP_KERNEL, allowing direct reclaim
> during the first MPOL_PREFERRED_MANY allocation attempt even though
> the caller clears __GFP_DIRECT_RECLAIM.

MPOL_PREFERRED_MANY is only used for the partner allocator. Without your
patches "mm: hugetlb: add CMA support for PMD-sized pages,"
cma_alloc_frozen_compound() is only used for huge page allocations. In
this case, I think we don't need the gfp flag, which is why I hardcoded
it, so there's no need for the Fixes tag; this patch should be part of
your new feature. Maybe I missed something?

> 
> Pass the caller's GFP mask through the helper so CMA respects its
> reclaim constraints when trying the preferred nodes.
> 
> Fixes: 9bda131c6093 ("mm: cma: add cma_alloc_frozen{_compound}()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Acked-by: Muchun Song <muchun.song@linux.dev>
> Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
> Reviewed-by: Oscar Salvador (SUSE) <osalvador@kernel.org>
> ---
>   include/linux/cma.h |  2 +-
>   mm/cma.c            | 10 ++++++++--
>   mm/hugetlb_cma.c    |  4 ++--
>   3 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/cma.h b/include/linux/cma.h
> index 8555d38a97b1a..4539ea5f2c4e8 100644
> --- a/include/linux/cma.h
> +++ b/include/linux/cma.h
> @@ -53,7 +53,7 @@ extern bool cma_release(struct cma *cma, const struct page *pages, unsigned long
>   
>   struct page *cma_alloc_frozen(struct cma *cma, unsigned long count,
>   		unsigned int align, bool no_warn);
> -struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order);
> +struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order, gfp_t gfp);
>   bool cma_release_frozen(struct cma *cma, const struct page *pages,
>   		unsigned long count);
>   
> diff --git a/mm/cma.c b/mm/cma.c
> index 9ec1d1fd5dff5..a7c47c0e7d070 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -933,9 +933,15 @@ struct page *cma_alloc_frozen(struct cma *cma, unsigned long count,
>   	return __cma_alloc_frozen(cma, count, align, gfp);
>   }
>   
> -struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order)
> +struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order, gfp_t gfp)
>   {
> -	gfp_t gfp = GFP_KERNEL | __GFP_COMP | __GFP_NOWARN;
> +	/*
> +	 * The only caller of cma_alloc_frozen_compound() is hugetlb, and
> +	 * hugetlb constructs its gfp mask via htlb_alloc_mask(), which already
> +	 * sets __GFP_COMP. Check here for usecases bypassing htlb_alloc_mask().
> +	 */
> +	if (WARN_ON_ONCE(!(gfp & __GFP_COMP)))
> +		return NULL;
>   
>   	return __cma_alloc_frozen(cma, 1 << order, order, gfp);
>   }
> diff --git a/mm/hugetlb_cma.c b/mm/hugetlb_cma.c
> index cd6a64986278a..3e5a30571524a 100644
> --- a/mm/hugetlb_cma.c
> +++ b/mm/hugetlb_cma.c
> @@ -69,14 +69,14 @@ struct folio *hugetlb_cma_alloc_frozen_folio(int order, gfp_t gfp_mask,
>   	}
>   
>   	if (hugetlb_cma[nid] && node_isset(nid, *nmask))
> -		page = cma_alloc_frozen_compound(hugetlb_cma[nid], order);
> +		page = cma_alloc_frozen_compound(hugetlb_cma[nid], order, gfp_mask);
>   
>   	if (!page && !(gfp_mask & __GFP_THISNODE)) {
>   		for_each_node_mask(node, *nmask) {
>   			if (node == nid || !hugetlb_cma[node])
>   				continue;
>   
> -			page = cma_alloc_frozen_compound(hugetlb_cma[node], order);
> +			page = cma_alloc_frozen_compound(hugetlb_cma[node], order, gfp_mask);
>   			if (page)
>   				break;
>   		}