Re: [PATCH v2 1/1] mm: numa_memblks: Identify the accurate NUMA ID of CFMW

[Cui Chao]

On 1/9/2026 5:35 PM, Pratyush Brahma wrote:
> On Fri, Jan 9, 2026 at 12:44 PM Cui Chao <cuichao1753@xxxxxxxxxxxxxx> wrote:
> > In some physical memory layout designs, the address space of CFMW
> > resides between multiple segments of system memory belonging to
> > the same NUMA node. In numa_cleanup_meminfo, these multiple segments
> > of system memory are merged into a larger numa_memblk. When
> > identifying which NUMA node the CFMW belongs to, it may be incorrectly
> > assigned to the NUMA node of the merged system memory.
> >
> > Example memory layout:
> >
> > Physical address space:
> >      0x00000000 - 0x1FFFFFFF  System RAM (node0)
> >      0x20000000 - 0x2FFFFFFF  CXL CFMW (node2)
> >      0x40000000 - 0x5FFFFFFF  System RAM (node0)
> >      0x60000000 - 0x7FFFFFFF  System RAM (node1)
> >
> > After numa_cleanup_meminfo, the two node0 segments are merged into one:
> >      0x00000000 - 0x5FFFFFFF  System RAM (node0) // CFMW is inside the range
> >      0x60000000 - 0x7FFFFFFF  System RAM (node1)
> >
> > So the CFMW (0x20000000-0x2FFFFFFF) will be incorrectly assigned to node0.
> >
> > To address this scenario, accurately identifying the correct NUMA node
> > can be achieved by checking whether the region belongs to both
> > numa_meminfo and numa_reserved_meminfo.
> >
> > Signed-off-by: Cui Chao <cuichao1753@xxxxxxxxxxxxxx>
> > Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
> > ---
> >   mm/numa_memblks.c | 5 +++--
> >   1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/numa_memblks.c b/mm/numa_memblks.c
> > index 5b009a9cd8b4..e91908ed8661 100644
> > --- a/mm/numa_memblks.c
> > +++ b/mm/numa_memblks.c
> > @@ -568,15 +568,16 @@ static int meminfo_to_nid(struct numa_meminfo *mi, u64 start)
> >   int phys_to_target_node(u64 start)
> >   {
> >          int nid = meminfo_to_nid(&numa_meminfo, start);
> > +       int reserved_nid = meminfo_to_nid(&numa_reserved_meminfo, start);
> >
> >          /*
> >           * Prefer online nodes, but if reserved memory might be
> >           * hot-added continue the search with reserved ranges.
> It would be good to change this comment as well. With the new logic
> you’re not just "continuing the search", you’re explicitly preferring
> reserved on overlap.
> Probably something like "Prefer numa_meminfo unless the address is
> also described by reserved ranges, in which case use the reserved
> nid."

Thanks.

I will revise the next version according to your suggestion.

> >           */
> > -       if (nid != NUMA_NO_NODE)
> > +       if (nid != NUMA_NO_NODE && reserved_nid == NUMA_NO_NODE)
> >                  return nid;
> >
> > -       return meminfo_to_nid(&numa_reserved_meminfo, start);
> > +       return reserved_nid;
> >   }
> >   EXPORT_SYMBOL_GPL(phys_to_target_node);
> >
> > --
> > 2.33.0
--
Best regards,
Cui Chao.