Re: [PATCH v4 2/6] mm: page_alloc: add __split_page()

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

On 2025/12/17 0:21, Zi Yan wrote:
> On 16 Dec 2025, at 6:48, 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>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>> ---
>>   include/linux/mmdebug.h | 10 ++++++++++
>>   mm/page_alloc.c         | 19 ++++++++++++-------
>>   2 files changed, 22 insertions(+), 7 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 da32397b4313..aa30d4436296 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -3077,6 +3077,15 @@ 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]
>> @@ -3089,14 +3098,12 @@ 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);
> 
> Could this be converted to VM_WARN_ON_PAGE() as well?

Yep, will change it too.

Thanks.

> 
> Otherwise, LGTM. Reviewed-by: Zi Yan <ziy@nvidia.com>
> 
> Best Regards,
> Yan, Zi
>