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

[Cui Chao]

Hi,

Thank you for your review.

On 12/30/2025 11:18 PM, Mike Rapoport wrote:
> Hi,
>
> On Tue, Dec 30, 2025 at 05:27:50PM +0800, Cui Chao 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. To address this
> Can you please provide an example of such memory layout?


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 this 
range
    0x60000000 - 0x7FFFFFFF  System RAM (node1)

So the CFMW (0x20000000-0x2FFFFFFF) will be incorrectly assigned to node0.


> > 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>
> > ---
> >   mm/numa_memblks.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/numa_memblks.c b/mm/numa_memblks.c
> > index 5b009a9cd8b4..1ef037f0e0e0 100644
> > --- a/mm/numa_memblks.c
> > +++ b/mm/numa_memblks.c
> > @@ -573,7 +573,8 @@ int phys_to_target_node(u64 start)
> >   	 * Prefer online nodes, but if reserved memory might be
> >   	 * hot-added continue the search with reserved ranges.
> >   	 */
> > -	if (nid != NUMA_NO_NODE)
> > +	if (nid != NUMA_NO_NODE &&
> > +		meminfo_to_nid(&numa_reserved_meminfo, start) == NUMA_NO_NODE)
> I'd suggest assigning the result of meminfo_to_nid(&numa_reserved_meminfo,
> start) to a local variable and using that in if and return statements.


I will use a local variable named reserved_nid.


> >   		return nid;
> >   
> >   	return meminfo_to_nid(&numa_reserved_meminfo, start);
> > --
> > 2.33.0
--
Best regards,
Cui Chao.