Re: [RFC PATCH 1/2] mm/fake-numa: fix under-allocation detection logic in uniform split

[Mike Rapoport <rppt@kernel.org>]

Hi,

On Tue, Apr 14, 2026 at 12:44:37AM +0900, Sang-Heon Jeon wrote:
> When split NUMA node uniformly, split_nodes_size_interleave_uniform()
> returns the next absolute node ID, not the number of nodes created.
> 
> The previous under-allocation detection logic compares next absolute node

I'd replace "previous" with "existing"

> ID (ret) and request count (n), which only works when nid starts at 0.
> 
> Fix under-allocation detection logic to compare the number of actually
> created nodes (ret - nid) against the request count (n).

It would be nice to have an example of memory configuration and
numa=fake=nU that demonstrates the issue.
 
> Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
> Reported-by: Donghyeon Lee <asd142513@gmail.com>
> Reported-by: Munhui Chae <mochae@student.42seoul.kr>
> Fixes: cc9aec03e58f ("x86/numa_emulation: Introduce uniform split capability") # 4.19
> ---
>  mm/numa_emulation.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/numa_emulation.c b/mm/numa_emulation.c
> index 703c8fa05048..e7f856c8f2a1 100644
> --- a/mm/numa_emulation.c
> +++ b/mm/numa_emulation.c
> @@ -416,7 +416,7 @@ void __init numa_emulation(struct numa_meminfo *numa_meminfo, int numa_dist_cnt)
>  					n, &pi.blk[0], nid);
>  			if (ret < 0)
>  				break;
> -			if (ret < n) {
> +			if (ret - nid < n) {
>  				pr_info("%s: phys: %d only got %d of %ld nodes, failing\n",
>  						__func__, i, ret, n);
>  				ret = -1;
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.