On Wed, Jan 13, 2021 at 09:56:49AM +0100, Oscar Salvador wrote:

On Mon, Jan 11, 2021 at 09:40:16PM +0200, Mike Rapoport wrote:

quoted

From: Mike Rapoport <redacted>

The first 4Kb of memory is a BIOS owned area and to avoid its allocation
for the kernel it was not listed in e820 tables as memory. As the result,
pfn 0 was never recognised by the generic memory management and it is not a
part of neither node 0 nor ZONE_DMA.

So, since it never was added to memblock.memory structs, it was not
initialized by init_unavailable_mem, right?

Actually it was initialized by init_unavailable_mem() and got zone=0 and
node=0, but the DMA zone started from pfn 1, so pfn 0 was never a part of
ZONE_DMA.
 

-- 
Oscar Salvador
SUSE L3

-- 
Sincerely yours,
Mike.