Re: [PATCH v4 5/6] mm: cma: add cma_alloc_frozen{_compound}()

[Zi Yan <ziy@nvidia.com>]

On 16 Dec 2025, at 6:48, Kefeng Wang wrote:

> Introduce cma_alloc_frozen{_compound}() helper to alloc pages without
> incrementing their refcount, then convert hugetlb cma to use the
> cma_alloc_frozen_compound() and cma_release_frozen() and remove the
> unused cma_{alloc,free}_folio(), also move the cma_validate_zones()
> into mm/internal.h since no outside user.
>
> The set_pages_refcounted() is only called to set non-compound pages
> after above changes, so remove the processing about PageHead.
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>  include/linux/cma.h | 26 ++++++------------------
>  mm/cma.c            | 48 +++++++++++++++++++++++++--------------------
>  mm/hugetlb_cma.c    | 24 +++++++++++++----------
>  mm/internal.h       | 10 +++++-----
>  4 files changed, 52 insertions(+), 56 deletions(-)
>
> diff --git a/include/linux/cma.h b/include/linux/cma.h
> index e5745d2aec55..e2a690f7e77e 100644
> --- a/include/linux/cma.h
> +++ b/include/linux/cma.h
> @@ -51,29 +51,15 @@ extern struct page *cma_alloc(struct cma *cma, unsigned long count, unsigned int
>  			      bool no_warn);
>  extern bool cma_release(struct cma *cma, const struct page *pages, unsigned long count);
>
> +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);
> +bool cma_release_frozen(struct cma *cma, const struct page *pages,
> +		unsigned long count);
> +
>  extern int cma_for_each_area(int (*it)(struct cma *cma, void *data), void *data);
>  extern bool cma_intersects(struct cma *cma, unsigned long start, unsigned long end);
>
>  extern void cma_reserve_pages_on_error(struct cma *cma);
>
> -#ifdef CONFIG_CMA
> -struct folio *cma_alloc_folio(struct cma *cma, int order, gfp_t gfp);
> -bool cma_free_folio(struct cma *cma, const struct folio *folio);
> -bool cma_validate_zones(struct cma *cma);
> -#else
> -static inline struct folio *cma_alloc_folio(struct cma *cma, int order, gfp_t gfp)
> -{
> -	return NULL;
> -}
> -
> -static inline bool cma_free_folio(struct cma *cma, const struct folio *folio)
> -{
> -	return false;
> -}
> -static inline bool cma_validate_zones(struct cma *cma)
> -{
> -	return false;
> -}
> -#endif
> -
>  #endif
> diff --git a/mm/cma.c b/mm/cma.c
> index 7f050cf24383..1aa1d821fbe9 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -856,8 +856,8 @@ static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr,
>  	return ret;
>  }
>
> -static struct page *__cma_alloc(struct cma *cma, unsigned long count,
> -		       unsigned int align, gfp_t gfp)
> +static struct page *__cma_alloc_frozen(struct cma *cma,
> +		unsigned long count, unsigned int align, gfp_t gfp)
>  {
>  	struct page *page = NULL;
>  	int ret = -ENOMEM, r;
> @@ -904,7 +904,6 @@ static struct page *__cma_alloc(struct cma *cma, unsigned long count,
>  	trace_cma_alloc_finish(name, page ? page_to_pfn(page) : 0,
>  			       page, count, align, ret);
>  	if (page) {
> -		set_pages_refcounted(page, count);
>  		count_vm_event(CMA_ALLOC_SUCCESS);
>  		cma_sysfs_account_success_pages(cma, count);
>  	} else {
> @@ -915,6 +914,21 @@ static struct page *__cma_alloc(struct cma *cma, unsigned long count,
>  	return page;
>  }
>
> +struct page *cma_alloc_frozen(struct cma *cma, unsigned long count,
> +		unsigned int align, bool no_warn)
> +{
> +	gfp_t gfp = GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0);
> +
> +	return __cma_alloc_frozen(cma, count, align, gfp);
> +}
> +
> +struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order)
> +{
> +	gfp_t gfp = GFP_KERNEL | __GFP_COMP | __GFP_NOWARN;
> +
> +	return __cma_alloc_frozen(cma, 1 << order, order, gfp);
> +}
> +
>  /**
>   * cma_alloc() - allocate pages from contiguous area
>   * @cma:   Contiguous memory region for which the allocation is performed.
> @@ -927,24 +941,18 @@ static struct page *__cma_alloc(struct cma *cma, unsigned long count,
>   */
>  struct page *cma_alloc(struct cma *cma, unsigned long count,
>  		       unsigned int align, bool no_warn)
> -{
> -	return __cma_alloc(cma, count, align, GFP_KERNEL | (no_warn ? __GFP_NOWARN : 0));
> -}
> -
> -struct folio *cma_alloc_folio(struct cma *cma, int order, gfp_t gfp)
>  {
>  	struct page *page;
>
> -	if (WARN_ON(!order || !(gfp & __GFP_COMP)))
> -		return NULL;
> -
> -	page = __cma_alloc(cma, 1 << order, order, gfp);
> +	page = cma_alloc_frozen(cma, count, align, no_warn);
> +	if (page)
> +		set_pages_refcounted(page, count);
>
> -	return page ? page_folio(page) : NULL;
> +	return page;
>  }
>
>  static bool __cma_release(struct cma *cma, const struct page *pages,
> -			  unsigned long count, bool compound)
> +			  unsigned long count, bool frozen)
>  {
>  	unsigned long pfn, end;
>  	int r;
> @@ -974,8 +982,8 @@ static bool __cma_release(struct cma *cma, const struct page *pages,
>  		return false;
>  	}
>
> -	if (compound)
> -		__free_pages((struct page *)pages, compound_order(pages));
> +	if (frozen)
> +		free_contig_frozen_range(pfn, count);
>  	else
>  		free_contig_range(pfn, count);

Can we get rid of free_contig_range() branch by making cma_release() put
each page’s refcount? Then, __cma_relase() becomes cma_release_frozen()
and the release pattern matches allocation pattern:
1. cma_alloc() calls cma_alloc_frozen() and manipulates page refcount.
2. cma_release() manipulates page refcount and calls cma_release_frozen().

The rest of changes looks good to me.

Best Regards,
Yan, Zi