On Thu 25-03-21 16:35:58, Michal Hocko wrote:
[...]
> So there is indeed a difference. One way around that would be to mark
> vmemmap pages (e.g. PageReserved && magic value stored somewhere in the
> struct page - resembling bootmem vmemmaps) or mark section fully backing
> vmemmaps as online (ugly).
I am not yet ready to give up on this. Here is a quick stab at the
pfn_to_online_page approach. It is not great but it is not really
terrible either. I think we can do better and skip
find_memory_block_by_id in most cases because nr_vmemmap_pages should be
constant with our current implementation.
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 754026a9164d..0d2bc22c29d3 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -304,8 +304,20 @@ struct page *pfn_to_online_page(unsigned long pfn)
return NULL;
ms = __nr_to_section(nr);
- if (!online_section(ms))
+ if (!online_section(ms)) {
+ if (memmap_on_memory) {
+ struct memory_block *mem;
+ unsigned long section_pfn = section_nr_to_pfn(nr);
+
+ mem = find_memory_block_by_id(memory_block_id(nr));
+ if (!mem || !mem->nr_vmemmap_pages || pfn - section_pfn
> mem->nr_vmemmap_pages)
+ return NULL;
+
+ return pfn_to_page(pfn);
+
+ }
return NULL;
+ }
/*
* Save some code text when online_section() +
--
Michal Hocko
SUSE Labs
