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

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Message-ID: <20260108161939.000026ec@huawei.com>
Date: Thu, 8 Jan 2026 16:19:39 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Cui Chao <cuichao1753@...tium.com.cn>
CC: Andrew Morton <akpm@...ux-foundation.org>, Mike Rapoport
	<rppt@...nel.org>, Wang Yinfeng <wangyinfeng@...tium.com.cn>,
	<linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>
Subject: Re: [PATCH v2 1/1] mm: numa_memblks: Identify the accurate NUMA ID
 of CFMW

On Tue, 6 Jan 2026 11:10:42 +0800
Cui Chao <cuichao1753@...tium.com.cn> 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@...tium.com.cn>

Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>

> ---
>  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.
>  	 */
> -	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);
>