From: Christoph Hellwig
Date: Sat Apr 28 2018 - 04:33:14 EST

On Fri, Apr 27, 2018 at 11:07:07AM -0500, Christopher Lameter wrote:
> Well it looks like what we are using it for is to force allocation from
> low physical memory if we fail to obtain proper memory through a normal
> channel. The use of ZONE_DMA is only there for emergency purposes.
> I think we could subsitute ZONE_DMA32 on x87 without a problem.
> Which means that ZONE_DMA has no purpose anymore.
> Can we make ZONE_DMA on x86 refer to the low 32 bit physical addresses
> instead and remove ZONE_DMA32?

While < 32-bit allocations are much more common there are plenty
of requirements for < 24-bit or other weird masks still.