On Tue, Aug 18, 2020 at 03:07:04PM +0800, chenzhou wrote:

On 2020/8/10 14:03, Dave Young wrote:

quoted

quoted

quoted

Previously I remember we talked about to use similar logic as X86, but I
remember you mentioned on some arm64 platform there could be no low
memory at all.  Is this not a problem now for the fallback?  Just be
curious, thanks for the update, for the common part looks good.

Did you mean this discuss: https://lkml.org/lkml/2019/12/27/122?

I meant about this reply instead :)
https://lkml.org/lkml/2020/1/16/616

Sorry for not repley in time, I was on holiday last week.

The platform James mentioned may exist for which have no devices and
need no low memory.

If there is no memory below 4GB, the arm64 kernel assumes that the
32-bit devices will have some DMA offsets shifting the addresses to the
bottom of the available RAM. So even if RAM starts above 4GB, we
ZONE_DMA32 will be allocated in the bottom 4GB of the high memory (and
if the hardware designers forgot to shift those DMA accesses, we don't
have to support the platform ;)).

So the arm64 notion of low memory differs slightly from the x86 one.

-- 
Catalin

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