Re: [PATCH 1/4] mm/page_alloc: always initialize memory map for the holes

[Guenter Roeck <linux@roeck-us.net>]

Hi,

On Wed, Jul 14, 2021 at 03:37:36PM +0300, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> Currently memory map for the holes is initialized only when SPARSEMEM
> memory model is used. Yet, even with FLATMEM there could be holes in the
> physical memory layout that have memory map entries.
> 
> For instance, the memory reserved using e820 API on i386 or
> "reserved-memory" nodes in device tree would not appear in memblock.memory
> and hence the struct pages for such holes will be skipped during memory map
> initialization.
> 
> These struct pages will be zeroed because the memory map for FLATMEM
> systems is allocated with memblock_alloc_node() that clears the allocated
> memory. While zeroed struct pages do not cause immediate problems, the
> correct behaviour is to initialize every page using __init_single_page().
> Besides, enabling page poison for FLATMEM case will trigger
> PF_POISONED_CHECK() unless the memory map is properly initialized.
> 
> Make sure init_unavailable_range() is called for both SPARSEMEM and FLATMEM
> so that struct pages representing memory holes would appear as PG_Reserved
> with any memory layout.
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>

This patch causes microblaze petalogix-ml605 qemu emulations to fail
silently (no console output). Reverting it fixes the problem.

Guenter

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# bad: [d2a572bf593a57246827bd79c91fe2ee6b7af1f0] mm/page_alloc: always initialize memory map for the holes
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# first bad commit: [d2a572bf593a57246827bd79c91fe2ee6b7af1f0] mm/page_alloc: always initialize memory map for the holes