Re: [PATCH] kho: add support for deferred struct page init

[Mike Rapoport <rppt@kernel.org>]

On Tue, Dec 16, 2025 at 10:05:27AM -0500, Pasha Tatashin wrote:
> > > +static struct page *__init kho_get_preserved_page(phys_addr_t phys,
> > > +                                               unsigned int order)
> > > +{
> > > +     unsigned long pfn = PHYS_PFN(phys);
> > > +     int nid = early_pfn_to_nid(pfn);
> > > +
> > > +     for (int i = 0; i < (1 << order); i++)
> > > +             init_deferred_page(pfn + i, nid);
> >
> > This will skip pages below node->first_deferred_pfn, we need to use
> > __init_page_from_nid() here.
> 
> Mike, but those struct pages should be initialized early anyway. If
> they are not yet initialized we have a problem, as they are going to
> be re-initialized later.

Can say I understand your point. Which pages should be initialized earlt?
And which pages will be reinitialized? 

> > > +
> > > +     return pfn_to_page(pfn);
> > > +}
> > > +
> > >  static void __init deserialize_bitmap(unsigned int order,
> > >                                     struct khoser_mem_bitmap_ptr *elm)
> > >  {
> > > @@ -449,7 +466,7 @@ static void __init deserialize_bitmap(unsigned int order,
> > >               int sz = 1 << (order + PAGE_SHIFT);
> > >               phys_addr_t phys =
> > >                       elm->phys_start + (bit << (order + PAGE_SHIFT));
> > > -             struct page *page = phys_to_page(phys);
> > > +             struct page *page = kho_get_preserved_page(phys, order);
> >
> > I think it's better to initialize deferred struct pages later in
> > kho_restore_page. deserialize_bitmap() runs before SMP and it already does
> 
> The KHO memory should still be accessible early in boot, right?

The memory is accessible. And we anyway should not use struct page for
preserved memory before kho_restore_{folio,pages}.
 
> > heavy lifting of memblock_reserve()s. Delaying struct page initialization
> > until restore makes it at least run in parallel with other initialization
> > tasks.
> >
> > I started to work on this just before plumbers and I have something
> > untested here:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git/log/?h=kho/deferred-page/v0.1
> >
> > >               union kho_page_info info;
> > >
> > >               memblock_reserve(phys, sz);
> > > --

-- 
Sincerely yours,
Mike.