Re: [PATCH v1 2/2] mm: factor out next_present_section_nr()

[Kirill A. Shutemov]

On Tue, Jan 14, 2020 at 11:49:19AM +0100, David Hildenbrand wrote:
> memmap_init_zone() is called for a physical memory region: pfn + size
> (nr_pages)
> 
> The highest possible PFN you can have is "-1(unsigned long) >>
> PFN_SHIFT". So even if you would want to add the very last section, the
> PFN would still be smaller than -1UL << PFN_SECTION_SHIFT.

PFN_SHIFT? I guess you mean PAGE_SHIFT.

Of course PFN can be more than -1UL >> PAGE_SHIFT. Like on 32-bit x86 with
PAE it is ((1ULL << 36) - 1) >> PAGE_SHIFT. That's the whole reason for
PAE.

The highest possible PFN must fit into phys_addr_t when shifted left by
PAGE_SHIFT and must fit into unsigned long. It's can be -1UL if
phys_addr_t is 64-bit.

Any other limitation I miss?

-- 
 Kirill A. Shutemov