Re: [PATCH v4 4/7] mm: page_owner: add support for splitting to any order in split page_owner.

[Zi Yan <ziy@nvidia.com>]

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On 14 Feb 2024, at 4:34, David Hildenbrand wrote:

> On 13.02.24 22:55, Zi Yan wrote:
>> From: Zi Yan <ziy@nvidia.com>
>>
>> It adds a new_order parameter to set new page order in page owner.
>> It prepares for upcoming changes to support split huge page to any
>> lower order.
>>
>> Signed-off-by: Zi Yan <ziy@nvidia.com>
>> ---
>>   include/linux/page_owner.h | 10 +++++-----
>>   mm/huge_memory.c           |  2 +-
>>   mm/page_alloc.c            |  4 ++--
>>   mm/page_owner.c            |  9 +++++----
>>   4 files changed, 13 insertions(+), 12 deletions(-)
>>
>> diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
>> index d7878523adfc..a784ba69f67f 100644
>> --- a/include/linux/page_owner.h
>> +++ b/include/linux/page_owner.h
>> @@ -11,7 +11,7 @@ extern struct page_ext_operations page_owner_ops;
>>   extern void __reset_page_owner(struct page *page, unsigned short order);
>>   extern void __set_page_owner(struct page *page,
>>   			unsigned short order, gfp_t gfp_mask);
>> -extern void __split_page_owner(struct page *page, int order);
>> +extern void __split_page_owner(struct page *page, int old_order, int new_order);
>>   extern void __folio_copy_owner(struct folio *newfolio, struct folio *old);
>>   extern void __set_page_owner_migrate_reason(struct page *page, int reason);
>>   extern void __dump_page_owner(const struct page *page);
>> @@ -31,10 +31,10 @@ static inline void set_page_owner(struct page *page,
>>   		__set_page_owner(page, order, gfp_mask);
>>   }
>>  -static inline void split_page_owner(struct page *page, int order)
>> +static inline void split_page_owner(struct page *page, int old_order, int new_order)
>>   {
>>   	if (static_branch_unlikely(&page_owner_inited))
>> -		__split_page_owner(page, order);
>> +		__split_page_owner(page, old_order, new_order);
>>   }
>>   static inline void folio_copy_owner(struct folio *newfolio, struct folio *old)
>>   {
>> @@ -56,11 +56,11 @@ static inline void reset_page_owner(struct page *page, unsigned short order)
>>   {
>>   }
>>   static inline void set_page_owner(struct page *page,
>> -			unsigned int order, gfp_t gfp_mask)
>> +			unsigned short order, gfp_t gfp_mask)
>>   {
>>   }
>>   static inline void split_page_owner(struct page *page,
>> -			int order)
>> +			int old_order, int new_order)
>>   {
>>   }
>>   static inline void folio_copy_owner(struct folio *newfolio, struct folio *folio)
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 3d30eccd3a7f..ad7133c97428 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -2919,7 +2919,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
>>   	unlock_page_lruvec(lruvec);
>>   	/* Caller disabled irqs, so they are still disabled here */
>>  -	split_page_owner(head, order);
>> +	split_page_owner(head, order, 0);
>>    	/* See comment in __split_huge_page_tail() */
>>   	if (PageAnon(head)) {
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 9d4dd41d0647..e0f107b21c98 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -2652,7 +2652,7 @@ void split_page(struct page *page, unsigned int order)
>>    	for (i = 1; i < (1 << order); i++)
>>   		set_page_refcounted(page + i);
>> -	split_page_owner(page, order);
>> +	split_page_owner(page, order, 0);
>>   	split_page_memcg(page, order, 0);
>>   }
>>   EXPORT_SYMBOL_GPL(split_page);
>> @@ -4837,7 +4837,7 @@ 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);
>> +		split_page_owner(page, order, 0);
>>   		split_page_memcg(page, order, 0);
>>   		while (page < --last)
>>   			set_page_refcounted(last);
>> diff --git a/mm/page_owner.c b/mm/page_owner.c
>> index 1319e402c2cf..ebbffa0501db 100644
>> --- a/mm/page_owner.c
>> +++ b/mm/page_owner.c
>> @@ -292,19 +292,20 @@ void __set_page_owner_migrate_reason(struct page *page, int reason)
>>   	page_ext_put(page_ext);
>>   }
>>  -void __split_page_owner(struct page *page, int order)
>> +void __split_page_owner(struct page *page, int old_order, int new_order)
>>   {
>>   	int i;
>>   	struct page_ext *page_ext = page_ext_get(page);
>>   	struct page_owner *page_owner;
>> -	unsigned int nr = 1 << order;
>> +	unsigned int old_nr = 1 << old_order;
>> +	unsigned int new_nr = 1 << new_order;
>>    	if (unlikely(!page_ext))
>>   		return;
>>  -	for (i = 0; i < nr; i++) {
>> +	for (i = 0; i < old_nr; i += new_nr) {
>>   		page_owner = get_page_owner(page_ext);
>> -		page_owner->order = 0;
>> +		page_owner->order = new_order;
>>   		page_ext = page_ext_next(page_ext);
>
> Staring at __set_page_owner_handle(), we do set all 1<<order page_exts (corresponding to 1<<order "struct page"s) to have ->order set.
>
> Wouldn't you have to do the same here?
>
> for (i = 0; i < 1 << old_order; i++) {
> 	page_owner = get_page_owner(page_ext);
> 	page_owner->order = new_order;
> 	page_ext = page_ext_next(page_ext);
> }

You are right. So page owner is per struct page. I misunderstood the code.
Thank you for pointing this out. Will fix it.


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Best Regards,
Yan, Zi

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