Re: [PATCH 2/2] mm/mm_init: drop overlap_memmap_init()

[Wei Yang <richard.weiyang@gmail.com>]

On Fri, Jun 26, 2026 at 10:40:32AM +0300, Mike Rapoport wrote:
>Hi Wei,
>
>On Thu, Jun 25, 2026 at 09:58:47AM +0000, Wei Yang wrote:
>> On Thu, Jun 25, 2026 at 10:39:40AM +0300, Mike Rapoport wrote:
>> >From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>> >
>> >When ZONE_NORMAL and ZONE_MOVABLE could overlap because kernelcore=mirror
>> >didn't reduce the span of ZONE_NORMAL, initialization of the memory map had
>> >to skip overlapping pages during initialization of ZONE_MOVABLE to avoid
>> >double initialization of the same struct pages.
>> >
>> >Since kernelcore=mirror works now the same way as other variants of
>> >kernelcore=/movablecore=, and adjusts the span of ZONE_NORMAL, there can't
>> >be an overlap between ZONE_NORMAL and ZONE_MOVABLE.
>> >
>> >Remove overlap_memmap_init().
>> >
>> 
>> Do you think this is valuable to mention the double init for the overlapped
>> range?
>
>Not sure I follow.
>We had this weird overlap_memmap_init() exactly to avoid double init.
> 

Yes, this is really weird.

As I described the detail in [1], before this change kernel would have
overlapped zone range like:

  Normal  [100000, 1c0000]
  Movable [140000, 1c0000]

Which means [140000, 1c0000] belongs to both Normal and Movable.
And memmap_init_range() would be called on this range twice for Normal and
Movable respectively. And we want overlap_memmap_init() could skip init this
to Normal. Because actually, the memory in this range belongs to Movable Zone.

But overlap_memmap_init() only would skip for Zone Movable. This means when
init to Zone Normal, it doesn't skip as we want. And when init to Zone
Movable, we don't expect it to skip.

[1]: https://lore.kernel.org/linux-mm/20260623092351.13031-3-richard.weiyang@gmail.com/

-- 
Wei Yang
Help you, Help me