Re: [PATCH] mm: Fix memblock_free_late() when using deferred struct page

[Mike Rapoport <rppt@kernel.org>]

On Wed, Feb 04, 2026 at 06:53:29AM +1100, Benjamin Herrenschmidt wrote:
> On Tue, 2026-02-03 at 20:40 +0200, Mike Rapoport wrote:
> > >  void __init memblock_free_pages(struct page *page, unsigned long pfn,
> > > -							unsigned int
> > > order)
> > > +				unsigned int order, bool reserved)
> > 
> > I've been thinking about after more coffee after our chat on IRC, and I
> > believe we don't need the bool reserved here.
> > 
> > Since the assumption that memblock_free_late() should be called only after
> > buddy is initialized, all the reserved pages should have their memmap setup
> > with PG_Reserved set. So we can use PageReserved() instead of passing the
> > boolean.
> 
> What about free_low_memory_core_early() -> 
>              __free_memory_core() ->
>                __free_pages_memory() ->
>                  memblock_free_pages() ?
> 
> I might be missing something but I don't see what would restrict this
> to the early pre-initialized struct pages other than that
> early_page_initialised() test, so we can't rely on anything in struct
> page inside memblock_free_pages().

Right, we can't rely on PG_Reserved being cleared for uninitialized pages :/

But I overlooked an easier and actually reliable way: use
free_reserved_area() instead of memblock_free_late().

> Cheers,
> Ben.

-- 
Sincerely yours,
Mike.