Re: [PATCH 0/8] Optional ZONE_DMA V1

[Martin Bligh <mbligh@google.com>]

Christoph Lameter wrote:
> On Tue, 12 Sep 2006, Jack Steiner wrote:
> 
> 
>>I'm missing something here. On Altix, currently ALL of the memory is reported
>>as being in the DMA zone:
>>
>>	% cat /proc/budd*
>>	Node 0, zone      DMA   3015    116      4      1    ...
>>	Node 1, zone      DMA   4243    355     15      3    ...
>>	Node 2, zone      DMA   4384    113      6      4    ...
>>
>>	% cat /proc/zoneinfo
>>	Node 0, zone      DMA
>>	  pages free     5868
>>	  ...
>>
>>The DMA slabs are empty, though.
> 
> 
> This is wrong. All memory should be in ZONE_NORMAL since we have no DMA 
> restrictions on Altix.

PPC64 works the same way, I believe. All memory is DMA'able, therefore 
it all fits in ZONE_DMA.

The real problem is that there's no consistent definition of what the
zones actually mean.

1. Is it DMA'able (this is stupid, as it doesn't say 'for what device'
2. Is it permanently mapped into kernel address space.

Given an inconsistent set of questions, it is unsuprising that we come
up with an inconsistent set of answers. We're trying to answer a 2D
question with a 1D answer.

What is really needed is to pass a physical address limit from the
caller, together with a flag that says whether the memory needs to be
mapped into the permanent kernel address space or not. The allocator
then finds the set of zones that will fulfill this criteria.
But I suspect this level of change will cause too many people to squeak
loudly.

M.