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

[Vlastimil Babka <vbabka@suse.cz>]

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?).