Re: [PATCH v2 1/3] mm/shuffle: don't move pages between zones and don't read garbage memmaps

David Hildenbrand
2020-06-23T07:39:34Z

> Hmm.. I thought this is the behavior for early section, while it looks current
> code doesn't work like this:
>
> if (section_is_early && memmap)
> free_map_bootmem(memmap);
> else
> depopulate_section_memmap(pfn, nr_pages, altmap);
>
> section_is_early is always "true" for early section, while memmap is not-NULL
> only when sub-section map is empty.
>
> If my understanding is correct, when we remove a sub-section in early section,
> the code would call depopulate_section_memmap(), which in turn free related
> memmap. By removing the memmap, the return value from pfn_to_online_page() is
> not a valid one.

I think you're right, and pfn_valid() would also return true, as it is
an early section. This looks broken.

>
> Maybe we want to write the code like this:
>
> if (section_is_early)
> if (memmap)
> free_map_bootmem(memmap);
> else
> depopulate_section_memmap(pfn, nr_pages, altmap);
>

I guess that should be the way to go

@Dan, I think what Wei proposes here is correct, right? Or how does it
work in the VMEMMAP case with early sections?

--
Thanks,

David / dhildenb