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

[Daniel Jordan]

On Thu, Jun 11, 2020 at 10:05:38AM -0700, Dave Hansen wrote:
> One other nit for this.  We *do* have actual hardware hotplug, and I'm
> pretty sure the alignment guarantees for hardware hotplug are pretty
> weak.  For instance, the alignment guarantees for persistent memory are
> still only 64MB even on modern platforms.
>
> Let's say we're on bare metal and we see an SRAT table that has some
> areas that show that hotplug might happen there.  Is this patch still
> ideal there?

Well, not if there's concern about hardware hotplug.

My assumption going in was that this wasn't a problem in practice.
078eb6aa50dc50 ("x86/mm/memory_hotplug: determine block size based on the end
of boot memory") was merged in 2018 to address qemu hotplug failures and >64G
systems have used a 2G block since 2014 with no complaints about alignment
issues, to my knowledge anyway.