linux-kernel - Re: [PATCH] mm: ignore nomap memory during mirror init

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Message-ID: <8d604308-36d3-4b55-8ddb-b33f8b586c1a@huawei.com>
Date: Fri, 18 Jul 2025 09:37:48 +0800
From: mawupeng <mawupeng1@...wei.com>
To: <rppt@...nel.org>
CC: <mawupeng1@...wei.com>, <akpm@...ux-foundation.org>, <ardb@...nel.org>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: ignore nomap memory during mirror init



On 2025/7/17 21:37, Mike Rapoport wrote:
> On Thu, Jul 17, 2025 at 07:06:52PM +0800, mawupeng wrote:
>>
>> On 2025/7/17 18:29, Mike Rapoport wrote:
>>> On Thu, Jul 17, 2025 at 04:57:23PM +0800, Wupeng Ma wrote:
>>>> When memory mirroring is enabled, the BIOS may reserve memory regions
>>>> at the start of the physical address space without the MR flag. This will
>>>> lead to zone_movable_pfn to be updated to the start of these reserved
>>>> regions, resulting in subsequent mirrored memory being ignored.
>>>>
>>>> Here is the log with efi=debug enabled:
>>>>   efi:   0x084004000000-0x0842bf37ffff [Conventional|   |  |MR|...|WB|WT|WC|  ]
>>>>   efi:   0x0842bf380000-0x0842c21effff [Loader Code |   |  |MR|...|WB|WT|WC|  ]
>>>>   efi:   0x0842c21f0000-0x0847ffffffff [Conventional|   |  |MR|...|WB|WT|WC|  ]
>>>>   efi:   0x085000000000-0x085fffffffff [Conventional|   |  |  |...|WB|WT|WC|  ]
>>>> ...
>>>>   efi:   0x084000000000-0x084003ffffff [Reserved    |   |  |  |...|WB|WT|WC|  ]
>>>>
>>>> Since this kind of memory can not be used by kernel. ignore nomap memory to fix
>>>> this issue.
>>
>> Since the first non-mirror pfn of this node is 0x084000000000, then zone_movable_pfn 
>> for this node will be updated to this. This will lead to Mirror Region 
>>   - 0x084004000000-0x0842bf37ffff
>>   - 0x0842bf380000-0x0842c21effff 
>>   - 0x0842c21f0000-0x0847ffffffff
>> be seen as non-mirror memory since zone_movable_pfn will be the start_pfn of this node
>> in adjust_zone_range_for_zone_movable().
> 
> What do you mean by "seen as non-mirror memory"?

It mean these memory range will be add to movable zone.

> 
> What is the problem with having movable zone on that node start at
> 0x084000000000?
> 
> Can you post the kernel log up to "Memory: nK/mK available" line for more
> context?

Memory: nK/mK available can not see be problem here, since there is nothing wrong
with the total memory. However this problem can be shown via lsmem --output-all

w/o this patch
[root@...alhost ~]# lsmem --output-all
RANGE                                  SIZE  STATE REMOVABLE         BLOCK NODE   ZONES
0x0000084000000000-0x00000847ffffffff   32G online       yes   67584-67839    0 Movable
0x0000085000000000-0x0000085fffffffff   64G online       yes   68096-68607    0 Movable

w/ this patch
[root@...alhost ~]# lsmem --output-all
RANGE                                  SIZE  STATE REMOVABLE         BLOCK NODE   ZONES
0x0000084000000000-0x00000847ffffffff   32G online       yes   8448-8479    0  Normal
0x0000085000000000-0x0000085fffffffff   64G online       yes   8512-8575    0 Movable


As shown above, All memory in this node is added to Zone Movable even some range of the memory
is mirror memory. With this patch, 0x0000084000000000-0x00000847ffffffff will be added to
zone normal as expected since the MR attribute.


>  
>> So igore nomap memory to fix this problem.
>>
>>>
>>> If the memory is nomap it won't be used by the kernel anyway.
>>> What's the actual issue you are trying to fix?
>>>  
>>>> Signed-off-by: Wupeng Ma <mawupeng1@...wei.com>
>>>> ---
>>>>  mm/mm_init.c | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/mm/mm_init.c b/mm/mm_init.c
>>>> index f2944748f526..1c36518f0fe4 100644
>>>> --- a/mm/mm_init.c
>>>> +++ b/mm/mm_init.c
>>>> @@ -405,7 +405,7 @@ static void __init find_zone_movable_pfns_for_nodes(void)
>>>>  		}
>>>>  
>>>>  		for_each_mem_region(r) {
>>>> -			if (memblock_is_mirror(r))
>>>> +			if (memblock_is_mirror(r) || memblock_is_nomap(r))
>>>>  				continue;
>>>>  
>>>>  			nid = memblock_get_region_node(r);
>>>> -- 
>>>> 2.43.0
>>>>
>>>
>>
>