RE: Increase default nodes shift to 10

From: Christoph Lameter <clameter_at_sgi.com>
Date: 2006-08-23 05:31:07
On Tue, 22 Aug 2006, Luck, Tony wrote:

> > Could we set these limits consitently to the largest IA64 configuration to 
> > make sure that a generic IA64 kernel is able to run on all machines?
> 
> We could ... but Horms has a good point that we might not
> want to do this if the cost is high.  Can you estimate how
> much memory will be allocated in these NR_CPUS and MAX_NUMNODES
> sized arrays.  If it is only[1] a couple of hundred Kbytes, then
> it might be worth it (even little IA-64 systems have 1GB, so
> 100K is 0.01%).

Worst case is probably the slab allocator.

The kmem_cache struct has pointer arrays per node and per cpu. If a 
corresponding cpu / node is not up then no further structures will be 
allocated.

pointers to per cpu caches array cache = NR_CPUS * sizeof(void *) = 8k.
	up from 64* sizeof(void *) = 512 byte.

pointers to per node l3 array = MAX_NUMNODES * sizeof(void *) = 8k.
	again up from currently 2k.

So additional overhead per slab is around 13k.  About 40 slabs. That 
results in ~520k additional overhead.
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Received on Wed Aug 23 05:31:55 2006

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