Re: [PATCH 0/3] bootmem2 III

[Johannes Weiner <hannes@saeurebad.de>]

Hi Andi,

Andi Kleen <andi@firstfloor.org> writes:

>> I was wondering yesterday if it would be feasible to enforce
>> contiguousness for nodes.
>
> And lose the memory? That would make people not happy.

No, one node descriptor per contiguous block on the physical node.

So this setup:

node 0: 0-2G, 4-6G
node 1: 2-4G, 6-8G

would have 4 pgdats.

>> So that arch-code does not create one pgdat
>> for each node but one for each contiguous block.  I have not yet looked
>> deeper into it, but I suspect that other mm code has similar problems
>> with nodes spanning other nodes.
>
> I wouldn't think so. At least sparse memory with large holes is not that
> uncommon in the non x86 world.

I do not quite understand.  Holes are not the problem - the overlapping
is.

The current bootmem allocator for example might pass the same pfn twice
to the buddy allocator when two nodes overlap.  And I don't know if
other mm code has the same problem.

	Hannes