Re: [PATCH v5 2/6] mm: page_alloc: add __split_page()

[Sid Kumar <sidhartha.kumar@oracle.com>]

On 12/30/25 1:24 AM, Kefeng Wang wrote:
> Factor out the splitting of non-compound page from make_alloc_exact()
> and split_page() into a new helper function __split_page().
>
> While at it, convert the VM_BUG_ON_PAGE() into a VM_WARN_ON_PAGE().
>
> Acked-by: David Hildenbrand <david@redhat.com>
> Acked-by: Muchun Song <muchun.song@linux.dev>
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>

Reviewed-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>

> ---
>   include/linux/mmdebug.h | 10 ++++++++++
>   mm/page_alloc.c         | 21 +++++++++++++--------
>   2 files changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
> index 14a45979cccc..ab60ffba08f5 100644
> --- a/include/linux/mmdebug.h
> +++ b/include/linux/mmdebug.h
> @@ -47,6 +47,15 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi);
>   			BUG();						\
>   		}							\
>   	} while (0)
> +#define VM_WARN_ON_PAGE(cond, page)		({			\
> +	int __ret_warn = !!(cond);					\
> +									\
> +	if (unlikely(__ret_warn)) {					\
> +		dump_page(page, "VM_WARN_ON_PAGE(" __stringify(cond)")");\
> +		WARN_ON(1);						\
> +	}								\
> +	unlikely(__ret_warn);						\
> +})
>   #define VM_WARN_ON_ONCE_PAGE(cond, page)	({			\
>   	static bool __section(".data..once") __warned;			\
>   	int __ret_warn_once = !!(cond);					\
> @@ -122,6 +131,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi);
>   #define VM_BUG_ON_MM(cond, mm) VM_BUG_ON(cond)
>   #define VM_WARN_ON(cond) BUILD_BUG_ON_INVALID(cond)
>   #define VM_WARN_ON_ONCE(cond) BUILD_BUG_ON_INVALID(cond)
> +#define VM_WARN_ON_PAGE(cond, page)  BUILD_BUG_ON_INVALID(cond)
>   #define VM_WARN_ON_ONCE_PAGE(cond, page)  BUILD_BUG_ON_INVALID(cond)
>   #define VM_WARN_ON_FOLIO(cond, folio)  BUILD_BUG_ON_INVALID(cond)
>   #define VM_WARN_ON_ONCE_FOLIO(cond, folio)  BUILD_BUG_ON_INVALID(cond)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 206397ed33a7..b9bfbb69537e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3080,6 +3080,15 @@ void free_unref_folios(struct folio_batch *folios)
>   	folio_batch_reinit(folios);
>   }
>   
> +static void __split_page(struct page *page, unsigned int order)
> +{
> +	VM_WARN_ON_PAGE(PageCompound(page), page);
> +
> +	split_page_owner(page, order, 0);
> +	pgalloc_tag_split(page_folio(page), order, 0);
> +	split_page_memcg(page, order);
> +}
> +
>   /*
>    * split_page takes a non-compound higher-order page, and splits it into
>    * n (1<<order) sub-pages: page[0..n]
> @@ -3092,14 +3101,12 @@ void split_page(struct page *page, unsigned int order)
>   {
>   	int i;
>   
> -	VM_BUG_ON_PAGE(PageCompound(page), page);
> -	VM_BUG_ON_PAGE(!page_count(page), page);
> +	VM_WARN_ON_PAGE(!page_count(page), page);
>   
>   	for (i = 1; i < (1 << order); i++)
>   		set_page_refcounted(page + i);
> -	split_page_owner(page, order, 0);
> -	pgalloc_tag_split(page_folio(page), order, 0);
> -	split_page_memcg(page, order);
> +
> +	__split_page(page, order);
>   }
>   EXPORT_SYMBOL_GPL(split_page);
>   
> @@ -5383,9 +5390,7 @@ static void *make_alloc_exact(unsigned long addr, unsigned int order,
>   		struct page *page = virt_to_page((void *)addr);
>   		struct page *last = page + nr;
>   
> -		split_page_owner(page, order, 0);
> -		pgalloc_tag_split(page_folio(page), order, 0);
> -		split_page_memcg(page, order);
> +		__split_page(page, order);
>   		while (page < --last)
>   			set_page_refcounted(last);
>