Re: [PATCH v3] mm/page_alloc: clear page->private in free_pages_prepare()

["David Hildenbrand (Arm)" <david@kernel.org>]

On 2/9/26 12:17, Vlastimil Babka wrote:
> On 2/7/26 23:08, David Hildenbrand (Arm) wrote:
>>>
>>> -               /*
>>> -                * page->private should not be set in tail pages. Fix up
>>> and warn once
>>> -                * if private is unexpectedly set.
>>> -                */
>>> -               if (unlikely(new_folio->private)) {
>>> -                       VM_WARN_ON_ONCE_PAGE(true, new_head);
>>> -                       new_folio->private = NULL;
>>> -               }
>>
>> BTW, I wonder whether we should bring that check back for non-device folios.
> 
> If the rule is now that when upon freeing in free_pages_prepare() we clear
> private in the head page and not tail pages (where we expect the owner of
> the page to do it), maybe that check for tail pages should be done in the
> is_check_pages_enabled() part of free_pages_prepare().
> 
> Or should the check be also in the split path because somebody can set a
> tail private between allocation and split? (and not just inherit it from a
> previous allocation that didn't clear it?).

We ran into that check in the past, when folio->X overlayed 
page->private in a tail, and would actually have to be zeroed out.

So it should be part of this splitting code I think.

-- 
Cheers,

David