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

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?