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

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Message-Id: <20260108094812.8757ce3ad8370668eaafb29c@linux-foundation.org>
Date: Thu, 8 Jan 2026 09:48:12 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Cui Chao <cuichao1753@...tium.com.cn>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>, 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.

Thanks.

Can you please help us understand the userspace-visible runtime effects
of this incorrect assignment?