Re: [PATCH v2 6/9] mm: page_alloc: add alloc_contig_frozen_pages()

[jane.chu@oracle.com]

On 9/2/2025 5:48 AM, Kefeng Wang wrote:
> Introduce a ACR_FLAGS_FROZEN flags to indicate that we want to
> allocate a frozen compound pages by alloc_contig_range(), also
> provide alloc_contig_frozen_pages() to allocate pages without
> incrementing their refcount, which may be beneficial to some
> users (eg hugetlb).
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>   include/linux/gfp.h |  6 ++++
>   mm/page_alloc.c     | 85 +++++++++++++++++++++++++--------------------
>   2 files changed, 54 insertions(+), 37 deletions(-)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 5ebf26fcdcfa..d0047b85fe34 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -427,6 +427,7 @@ extern gfp_t vma_thp_gfp_mask(struct vm_area_struct *vma);
>   typedef unsigned int __bitwise acr_flags_t;
>   #define ACR_FLAGS_NONE ((__force acr_flags_t)0) // ordinary allocation request
>   #define ACR_FLAGS_CMA ((__force acr_flags_t)BIT(0)) // allocate for CMA
> +#define ACR_FLAGS_FROZEN ((__force acr_flags_t)BIT(1)) // allocate for frozen compound pages
>   
>   /* The below functions must be run on a range from a single zone. */
>   extern int alloc_contig_range_noprof(unsigned long start, unsigned long end,
> @@ -437,6 +438,11 @@ extern struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_
>   					      int nid, nodemask_t *nodemask);
>   #define alloc_contig_pages(...)			alloc_hooks(alloc_contig_pages_noprof(__VA_ARGS__))
>   
> +struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages,
> +		gfp_t gfp_mask, int nid, nodemask_t *nodemask);
> +#define alloc_contig_frozen_pages(...) \
> +	alloc_hooks(alloc_contig_frozen_pages_noprof(__VA_ARGS__))
> +
>   #endif
>   void free_contig_range(unsigned long pfn, unsigned long nr_pages);
>   
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index baead29b3e67..0677c49fdff1 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6854,6 +6854,9 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
>   	if (__alloc_contig_verify_gfp_mask(gfp_mask, (gfp_t *)&cc.gfp_mask))
>   		return -EINVAL;
>   
> +	if ((alloc_flags & ACR_FLAGS_FROZEN) && !(gfp_mask & __GFP_COMP))
> +		return -EINVAL;
> +
>   	/*
>   	 * What we do here is we mark all pageblocks in range as
>   	 * MIGRATE_ISOLATE.  Because pageblock and max order pages may
> @@ -6951,7 +6954,8 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
>   
>   		check_new_pages(head, order);
>   		prep_new_page(head, order, gfp_mask, 0);
> -		set_page_refcounted(head);
> +		if (!(alloc_flags & ACR_FLAGS_FROZEN))
> +			set_page_refcounted(head);
>   	} else {
>   		ret = -EINVAL;
>   		WARN(true, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n",
> @@ -6963,15 +6967,6 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
>   }
>   EXPORT_SYMBOL(alloc_contig_range_noprof);
>   
> -static int __alloc_contig_pages(unsigned long start_pfn,
> -				unsigned long nr_pages, gfp_t gfp_mask)
> -{
> -	unsigned long end_pfn = start_pfn + nr_pages;
> -
> -	return alloc_contig_range_noprof(start_pfn, end_pfn, ACR_FLAGS_NONE,
> -					 gfp_mask);
> -}
> -
>   static bool pfn_range_valid_contig(struct zone *z, unsigned long start_pfn,
>   				   unsigned long nr_pages)
>   {
> @@ -7003,31 +6998,8 @@ static bool zone_spans_last_pfn(const struct zone *zone,
>   	return zone_spans_pfn(zone, last_pfn);
>   }
>   
> -/**
> - * alloc_contig_pages() -- tries to find and allocate contiguous range of pages
> - * @nr_pages:	Number of contiguous pages to allocate
> - * @gfp_mask:	GFP mask. Node/zone/placement hints limit the search; only some
> - *		action and reclaim modifiers are supported. Reclaim modifiers
> - *		control allocation behavior during compaction/migration/reclaim.
> - * @nid:	Target node
> - * @nodemask:	Mask for other possible nodes
> - *
> - * This routine is a wrapper around alloc_contig_range(). It scans over zones
> - * on an applicable zonelist to find a contiguous pfn range which can then be
> - * tried for allocation with alloc_contig_range(). This routine is intended
> - * for allocation requests which can not be fulfilled with the buddy allocator.
> - *
> - * The allocated memory is always aligned to a page boundary. If nr_pages is a
> - * power of two, then allocated range is also guaranteed to be aligned to same
> - * nr_pages (e.g. 1GB request would be aligned to 1GB).
> - *
> - * Allocated pages can be freed with free_contig_range() or by manually calling
> - * __free_page() on each allocated page.
> - *
> - * Return: pointer to contiguous pages on success, or NULL if not successful.
> - */
> -struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_mask,
> -				 int nid, nodemask_t *nodemask)
> +static struct page *__alloc_contig_pages(unsigned long nr_pages, gfp_t gfp_mask,
> +		acr_flags_t alloc_flags, int nid, nodemask_t *nodemask)
>   {
>   	unsigned long ret, pfn, flags;
>   	struct zonelist *zonelist;
> @@ -7050,8 +7022,8 @@ struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_mask,
>   				 * and cause alloc_contig_range() to fail...
>   				 */
>   				spin_unlock_irqrestore(&zone->lock, flags);
> -				ret = __alloc_contig_pages(pfn, nr_pages,
> -							gfp_mask);
> +				ret = alloc_contig_range_noprof(pfn, pfn + nr_pages,
> +							alloc_flags, gfp_mask);
>   				if (!ret)
>   					return pfn_to_page(pfn);
>   				spin_lock_irqsave(&zone->lock, flags);
> @@ -7062,6 +7034,45 @@ struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_mask,
>   	}
>   	return NULL;
>   }
> +
> +/**
> + * alloc_contig_pages() -- tries to find and allocate contiguous range of pages
> + * @nr_pages:	Number of contiguous pages to allocate
> + * @gfp_mask:	GFP mask. Node/zone/placement hints limit the search; only some
> + *		action and reclaim modifiers are supported. Reclaim modifiers
> + *		control allocation behavior during compaction/migration/reclaim.
> + * @nid:	Target node
> + * @nodemask:	Mask for other possible nodes
> + *
> + * This routine is a wrapper around alloc_contig_range(). It scans over zones
> + * on an applicable zonelist to find a contiguous pfn range which can then be
> + * tried for allocation with alloc_contig_range(). This routine is intended
> + * for allocation requests which can not be fulfilled with the buddy allocator.
> + *
> + * The allocated memory is always aligned to a page boundary. If nr_pages is a
> + * power of two, then allocated range is also guaranteed to be aligned to same
> + * nr_pages (e.g. 1GB request would be aligned to 1GB).
> + *
> + * Allocated pages can be freed with free_contig_range() or by manually calling
> + * __free_page() on each allocated page.
> + *
> + * Return: pointer to contiguous pages on success, or NULL if not successful.
> + */
> +struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_mask,
> +		int nid, nodemask_t *nodemask)
> +{
> +	return __alloc_contig_pages(nr_pages, gfp_mask, ACR_FLAGS_NONE,
> +				    nid, nodemask);
> +}
> +
> +struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages,
> +		gfp_t gfp_mask, int nid, nodemask_t *nodemask)
> +{
> +	/* always allocate compound pages without refcount increased */
> +	return __alloc_contig_pages(nr_pages, gfp_mask | __GFP_COMP,
> +				    ACR_FLAGS_FROZEN, nid, nodemask);
> +}
> +
>   #endif /* CONFIG_CONTIG_ALLOC */
>   
>   void free_contig_range(unsigned long pfn, unsigned long nr_pages)

Looks good!  Thanks for your work, this makes the frozen page allocation 
explicitly stated.

Reviewed-by: Jane Chu <jane.chu@oralce.com>

-jane