Re: [LSF/MM/BPF TOPIC][RFC PATCH v4 00/27] Private Memory Nodes (w/ Compressed RAM)

[Gregory Price]

On Wed, Jun 03, 2026 at 03:00:01PM +1000, Balbir Singh wrote:
> > 
> >    __GFP_THISNODE cannot be overloaded to do anything useful here.
> 
> Let me clarify, I meant to say, let's use a nodemask for allocation
> and __GFP_THISNODE gets us to the node we desire, if that is the only
> node. My earlier comment might not have been clear.
> 

I've been tested an stripped back patch set where I drop all FALLBACK
entries for private nodes (including for itself) and only keep the
NOFALLBACK entry for private nodes.

This effectively isolates the nodes for any allocation without
__GFP_THISNODE.

This also precludes these nodes from ever using non-mbind mempolicies,
which I think is a completely reasonable compromise and something I was
already expecting we would do.

Notably: slub.c injects __GFP_THISNODE internally on behalf of kmalloc,
which causes spillage into private nodes because slub allows private
nodes in its mask.  I think this is fixable.

I have to inspect some other __GFP_THISNODE users (hugetlb, some arch
code, etc), but it seems like fully dropping the FALLBACK entries and
requiring __GFP_THISNODE might be sufficient.

~Gregory