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

[Balbir Singh]

On Wed, Jun 10, 2026 at 06:41:57AM -0400, Gregory Price wrote:
> 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.
> 

Agreed.

> 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

That's good progress, thanks for the update!

Balbir