Re: [PATCH 4/7] ppc64 - Specify amount of kernel memory at boot time

[Joel Schopp <jschopp@austin.ibm.com>]

>> This patch adds the kernelcore= parameter for ppc64.
>>
>> The amount of memory will requested will not be reserved in all nodes. The
>> first node that is found that can accomodate the requested amount of memory
>> and have remaining more for ZONE_EASYRCLM is used. If a node has memory holes,
>> it also will not be used.
> 
> One thing I think we really need to see before these go into mainline is
> the ability to shrink the ZONE_EASYRCLM at runtime, and give the memory
> back to NORMAL/DMA.
> 
> Otherwise, any system starting off sufficiently small will end up having
> lowmem starvation issues.  Allowing resizing at least gives the admin a
> chance to avoid those issues.
> 

I'm not too keen on calling it resizing, because that term is 
misleading.  The resizing is one way.  You can't later resize back. It's 
like a window that you can only close but never reopen.  We should call 
it "runtime incremental disabling", or RID.

I don't think we need RID in order to merge these patches.  RID can be 
merged later if people decide they want a special easy reclaim zone that 
could disappear at any moment.  I personally fall in the camp of wanting 
my zones I explicitly enabled to stay put and am opposed to RID.

If only somebody had presented a solution that was flexible enough to 
dynamically resize reclaimable and non-reclaimable both ways.
http://sourceforge.net/mailarchive/message.php?msg_id=13864331