On Fri, Dec 19, 2025 at 4:19 AM Mike Rapoport <[email protected]> wrote: > > On Tue, Dec 16, 2025 at 10:36:01AM -0500, Pasha Tatashin wrote: > > On Tue, Dec 16, 2025 at 10:19 AM Mike Rapoport <[email protected]> wrote: > > > > > > 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? > > > > All pages below node->first_deferred_pfn. > > > > > And which pages will be reinitialized? > > > > kho_memory_init() is called after free_area_init() (which calls > > memmap_init_range to initialize low memory struct pages). So, if we > > use __init_page_from_nid() as suggested, we would be blindly running > > __init_single_page() again on those low-memory pages that > > memmap_init_range() already set up. This would cause double > > initialization and corruptions due to losing the order information. > > > > > > > > + > > > > > > + 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}. > > > > This makes sense, what happens if someone calls kho_restore_folio() > > before deferred pages are initialized? > > That's fine, because this memory is still memblock_reserve()ed and deferred > init skips reserved ranges. > There is a problem however with the calls to kho_restore_{pages,folio}() > after memblock is gone because we can't use early_pfn_to_nid() then.
I agree with the regarding memblock and early_pfn_to_nid(), but I don't think we need to rely on early_pfn_to_nid() during the restore phase. > I think we can start with Evangelos' approach that initializes struct pages > at deserialize time and then we'll see how to optimize it. Let's do the lazy tail initialization that I proposed to you in a chat: we initialize only the head struct page during deserialize_bitmap(). Since this happens while memblock is still active, we can safely use early_pfn_to_nid() to set the nid in the head page's flags, and also preserve order as we do today. Then, we can defer the initialization of all tail pages to kho_restore_folio(). At that stage, we no longer need memblock or early_pfn_to_nid(); we can simply inherit the nid from the head page using page_to_nid(head). This approach seems to give us the best of both worlds: It avoids the memblock dependency during restoration. It keeps the serial work in deserialize_bitmap() to a minimum (O(1)O(1) per region). It allows the heavy lifting of tail page initialization to be done later in the boot process, potentially in parallel, as you suggested. Thanks, Pasha
