[PATCH RFC 04/29] mm/page_alloc: allow for making page types sticky until freed
David Hildenbrand
david at redhat.com
Tue Jun 24 01:27:47 AEST 2025
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
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