Re: [PATCH v2] x86/mm: use max memory block size on bare metal

[Daniel Jordan]

On Thu, Jun 11, 2020 at 07:16:02AM -0700, Dave Hansen wrote:
> On 6/9/20 3:54 PM, Daniel Jordan wrote:
> > +	/*
> > +	 * Use max block size to minimize overhead on bare metal, where
> > +	 * alignment for memory hotplug isn't a concern.
> > +	 */
> > +	if (hypervisor_is_type(X86_HYPER_NATIVE)) {
> > +		bz = MAX_BLOCK_SIZE;
> > +		goto done;
> > +	}
> 
> What ends up being the worst case scenario?  Booting a really small
> bare-metal x86 system, say with 64MB or 128MB of RAM?  What's the
> overhead there?

Might not be following you, so bear with me, but we only get to this check on a
system with a physical address end of at least MEM_SIZE_FOR_LARGE_BLOCK (64G),
and this would still (ever so slightly...) reduce overhead of memory block init
at boot in that case.