[PATCH RFC 04/29] mm/page_alloc: allow for making page types sticky until freed

[David Hildenbrand]

On 18.06.25 20:43, Zi Yan wrote:
> On 18 Jun 2025, at 13:39, David Hildenbrand wrote:
> 
>> Let's allow for not clearing a page type before freeing a page to the
>> buddy.
>>
>> We'll focus on having a type set on the first page of a larger
>> allocation only.
>>
>> With this change, we can reliably identify typed folios even though
>> they might be in the process of getting freed, which will come in handy
>> in migration code (at least in the transition phase).
>>
>> Signed-off-by: David Hildenbrand <david at redhat.com>
>> ---
>>   mm/page_alloc.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 858bc17653af9..44e56d31cfeb1 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1380,6 +1380,9 @@ __always_inline bool free_pages_prepare(struct page *page,
>>   			mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1);
>>   		page->mapping = NULL;
>>   	}
>> +	if (unlikely(page_has_type(page)))
>> +		page->page_type = UINT_MAX;
>> +
>>   	if (is_check_pages_enabled()) {
>>   		if (free_page_is_bad(page))
>>   			bad++;
> 
> Should we be pedantic to only do this for PageOffline and PageZsmalloc
> and warn for the rest page types?

I think we should just allow any page types. Limiting it to specific 
types sounds like some use-after-free check that probably shouldn't be 
handled that way.

-- 
Cheers,

David / dhildenb