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

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Message-ID: <0e1e1b5f-df0c-459d-9cba-5bde5ad56ba3@phytium.com.cn>
Date: Thu, 15 Jan 2026 18:06:45 +0800
From: Cui Chao <cuichao1753@...tium.com.cn>
To: Pratyush Brahma <pratyush.brahma@....qualcomm.com>
Cc: Wang Yinfeng <wangyinfeng@...tium.com.cn>, linux-cxl@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>,
 Jonathan Cameron <jonathan.cameron@...wei.com>,
 Mike Rapoport <rppt@...nel.org>
Subject: Re: [PATCH v2 1/1] mm: numa_memblks: Identify the accurate NUMA ID of
 CFMW


On 1/9/2026 5:35 PM, Pratyush Brahma wrote:
> On Fri, Jan 9, 2026 at 12:44 PM 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.
> 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.