From: Zoltan Menyhart <>
Date: 2006-11-30 21:47:09
>> Do we need a "max_order" variable that could be adjusted to some lower
>> value that MAX_ORDER if we find the memory topology doesn't fit inside
>> the lines?  
> (Your email talks about nodes, but I am asuming that we're actually dealing
> with per-zone concepts here)

...and ...

> But I wonder if a better approach would be to teach ia64 to just throw away
> the last 1 ..  MAX_ORDER-1 pages from the oddball zone?

Assume we've got a machine with a memory configuration:

Node 0:		0 ... 4 Gbyte - 1
Node 1:		4 Gbyte ... 16 Gbyte - 1

Assume MAX_ORDER is 8 Gbytes (a single binary, for all of our machines,
for maintenance reasons).

An allocation of 8 Gbytes should have its chance.
Therefore the global MAX_ORDER should not be diminished dynamically.
Surely we do not want to throw away 4 Gbytes of memory.

The kernel should support that both of the nodes have starting address at 0.
Therefore the "node_bootmem_map"-s of both of the nodes include the address
range 0 ... 4 Gbyte in the example above.
The "node_bootmem_map" of node 1 just happens to contain 0-s in the range
of 0 ... 4 Gbyte.

A not-in-use level of the buddy allocator
(the 8 Gbyte level on node 0 in the example above)
does not cost too much, I think there is no use to add complexity to the
allocator code.


Zoltan Menyhart

P.S. I guess it is not an ia64-only issue.

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Received on Thu Nov 30 21:47:32 2006

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