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

[Gregory Price <gourry@gourry.net>]

On Wed, Feb 25, 2026 at 12:40:09PM +0000, Alejandro Lucero Palau wrote:
> 
> I can see the nid param is just a "preferred nid" with alloc pages. Using
> __GFP_PRIVATE will restrict the allocation to private nodes but I think the
> idea here is:
> 
> 
> 1) I own this node
> 
> 2) Do not give me memory from another private node but from mine.
> 
> 

I mildly mis-read this question, apologies.

Multiple private nodes in the nodemask are ignored, because the nodemask
is a filter function for the fallback lists - and private nodes never
show up in the fallback lists (except for their own).

So for example

Nodes:  Normal(A,B), Private(C,D)

Fallback lists:
   A:   [A,B]
   B:   [B,A]
   C:   [C,A,B]
   D:   [D,B,A]

            combination                       |  possible result
----------------------------------------------------------------
__GFP_PRIVATE + pref_node(C) + nodemask(NULL) = (C or A or B)
__GFP_PRIVATE + pref_node(C) + nodemask(C,D)  = C
GFP_PRIVATE + pref_node(C) + nodemask(ALL)    = C

Basically private nodes are completely ignored in the nodemask, so you
cannot do fallback allocations to other private nodes.

There is no good abstraction (that I have found) to communicate
multi-private-node allocations simply because this would imply needing
private nodes to be in the fallback lists for other nodes.

Maybe there is a possibility of modifying fallback lists explicitly, but
I think that is out of scope for the first implementation.

~Gregory