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

[mawupeng <mawupeng1@huawei.com>]

On 2025/7/20 20:38, Mike Rapoport wrote:
> On Fri, Jul 18, 2025 at 09:37:48AM +0800, mawupeng wrote:
>>
>>
>> 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
> 
> I didn't ask for that particular line but for *up to that line*.
>  
>> w/o this patch
>> [root@localhost ~]# 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@localhost ~]# 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 I see the problem, you have a problematic firmware that fails to report
> memory as mirrored because it reserved for firmware own use. This causes
> for non-mirrored memory to appear before mirrored memory. And this breaks
> an assumption in find_zone_movable_pfns_for_nodes() that mirrored memory
> always has lower addresses than non-mirrored memory and you end up wiht
> having all the memory in movable zone.

Yes.

> 
> So to workaround this firmware issue you propose a hack that would skip
> NOMAP regions while calculating zone_movable_pfn because your particular
> firmware reports the reserved mirrored memory as NOMAP.
> 
> Why don't you simply pass "kernelcore=32G" on the command line and you'll
> get the same result.

Since mirrored memory are in each node, not only one, "kernelcore=32G" can
not fix this problem.

Since nomap memory can not be used by kernel anyway. AFICT ignore this during
mirror memory init is the right thing to do.

> 
>> 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.
>