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

[Dave Hansen]

On Thu, 2006-02-23 at 18:01 +0000, Mel Gorman wrote:
> On Thu, 23 Feb 2006, Dave Hansen wrote:
> > OK, back to the hapless system admin using kernelcore. They have a
> > 4-node system with 2GB of RAM in each node for 8GB total.  They use
> > kernelcore=1GB.  They end up with 4x1GB ZONE_DMA and 4x1GB
> > ZONE_EASYRCLM.  Perfect.  You can safely remove 4GB of RAM.
> >
> > Now, imagine that the machine has been heavily used for a while, there
> > is only 1 node's memory available, but CPUs are available in the same
> > places as before.  So, you start up your partition again have 8GB of
> > memory in one node.  Same kernelcore=1GB option.  You get 1x7GB ZONE_DMA
> > and 1x1GB ZONE_EASYRCLM.  I'd argue this is going to be a bit of a
> > surprise to the poor admin.
> >
> 
> That sort of surprise is totally unacceptable but the behaviour of 
> kernelcore needs to be consistent on both the x86 and the ppc (any any 
> other ar. How about;
> 
> 1. kernelcore=X determines the total amount of memory for !ZONE_EASYRCLM
>     (be it ZONE_DMA, ZONE_NORMAL or ZONE_HIGHMEM)

Sounds reasonable.  But, if you're going to do that, should we just make
it the opposite and explicitly be easy_reclaim_mem=?  Do we want the
limit to be set as "I need this much kernel memory", or "I want this
much removable memory".  I dunno.

> 2. For every node that can have ZONE_EASYRCLM, split the kernelcore across
>     the nodes as a percentage of the node size
> 
>     Example: 4 nodes, 1 GiB each, kernelcore=512MB
>  		node 0 ZONE_DMA = 128MB
>  		node 1 ZONE_DMA = 128MB
>  		node 2 ZONE_DMA = 128MB
>  		node 3 ZONE_DMA = 128MB
> 
>  	    2 nodes, 3GiB and 1GIB, kernelcore=512MB
>  		node 0 ZONE_DMA = 384
>  		node 1 ZONE_DMA = 128
> 
> It gets a bit more complex on NUMA for x86 because ZONE_NORMAL is 
> involved but the idea would essentially be the same.

Yes, chopping it up seems like the right thing (or as close as we can
get) to me.  

-- Dave

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