Re: CXL Boot to Bash - Section 3: Memory (block) Hotplug

[David Hildenbrand]

On 20.02.25 19:43, Gregory Price wrote:
> On Thu, Feb 20, 2025 at 09:50:07AM -0800, Yang Shi wrote:
> > > > I will double check that this isn't working as expected, and i'll double
> > > > check for a build option as well.
> > > >
> > > > stupid question - it sorta seems like you'd want this as the default
> > > > setting for driver-managed hotplug memory blocks, but I suppose for
> > > > very small blocks there's problems (as described in the docs).
> > >
> > > The issue is that it is per-memblock. So you'll never have 1 GiB ranges
> > > of consecutive usable memory (e.g., 1 GiB hugetlb page).
> >
> > Regardless of ZONE_MOVABLE or ZONE_NORMAL, right?
> >
> > Thanks,
> > Yang
>
>  From my testing, yes.

Yes, the only way to get some 1 GiB pages is by using larger memory 
blocks (e.g., 2 GiB on x86-64), which comes with a different set of 
issues (esp. hotplug granularity).

Of course, only 1x usable 1 GiB page for each 2 GiB block.

There were ideas in how to optimize that (e.g., requiring  a new sysfs 
interface to expose variable-sized blocks), if anybody is interested, 
please reach out.

--
Cheers,

David / dhildenb