Re: [RFC] [PATCH] more support for memory-less-node.

["Martin J. Bligh" <mbligh@mbligh.org>]

Andi Kleen wrote:
>> I wasn't suggesting having NULL pointers for pgdats, if that's what you
>> mean. 
> 
> That is what started the original thread at least. Can happen on some
> ia64 platforms.

OK, that does seem kind of ugly.

>> Just nodes with no memory in them, the pgdat would still be there. 
>> pgdat = struct node, except everything's badly named.
> 
> Ok those can happen even on x86-64, mostly because it's possible
> to fill up a node early during boot up with bootmem and then
> it's effectively empty.
> 
> [there is even still a open bug when this happens on node 0]
>  
> Handling out of memory here of course has to be always done.

Yup, if we just set the "size" of the node to zero, it seems
like a natural degenerate case that should be handled anyway.

> Just NULL pointers in core data structures are evil. But I'm glad we 
> agree here.
> 
> Now if it's better to set up a empty node or use a nearby node
> for a memory less cpu can be further discussed. I still think
> I lean towards the later.

Just seems kind of ugly and unnecessary, particularly if that
memory-less cpu (or IO node) is equidistant from one or more
memory-possessing nodes. As long as their zonelist is set up
correctly, it should all work fine without that, right?

build_zonelists_node already checks populated_zone() so it looks
like it's all set up for that already ...

M.