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

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Message-ID: <9688e968-e9af-4143-b550-16c02a0b4ceb@huawei.com>
Date: Thu, 17 Jul 2025 19:06:52 +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 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().

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
>>
>