Re: [Lhms-devel] [RFC] fix for hot-add enabled SRAT/BIOS and numa KVA areas

Dave Hansen
2004-11-18T02:24:06Z

On Wed, 2004-11-17 at 18:08, keith wrote:
> I am not anticipating to support hot-add without config_nonlinear or
> something similar which should provide more flexibility in allocation of
> smaller section mem_maps. This is only a issue when booted as a
> discontig system. We don't even consult the SRAT when we boot flat
> (contiguous address space) so it is a non-issue.

Once a system has been running for any length of time, finding any
multi-order pages gets somewhat hard. For a 16M section, you're still
talking about ~128k of mem_map, which is still an order 5 allocation.
Nick's kswapd higher-order patches should help with this, though.

> Wasting 500k of lowmem for memory that "might" be there is no good. I
> don't think having to preallocate the mem_map for a hot-add is really
> that good. What if the system never adds memory? What if it only adds
> 8gig not 49g? The system is crippled because it reserves the lmem_map
> it "might" do a hot add with?

I have the feeling we'll eventually need a boot-time option for this
reservation. Your patch, of course will work for now. Do you want me
to pick it up in my tree?

> I forgot the mention that without this patch my system does not boot
> with the hot-add support enabled in the bios.

Why not? I'm just curious what caused the actual failure.

-- Dave