Re: [PATCH v2 2/3] mm/memory_hotplug: split memmap_on_memory requests across memblocks

David Hildenbrand
2023-08-14T07:21:41Z

On 14.08.23 08:45, Huang, Ying wrote:
> "Verma, Vishal L" <vishal.l.verma@intel.com> writes:
>
>> On Mon, 2023-07-24 at 13:54 +0800, Huang, Ying wrote:
>>> Vishal Verma <vishal.l.verma@intel.com> writes:
>>>
>>>>
>>>> @@ -2035,12 +2056,38 @@ void try_offline_node(int nid)
>>>> }
>>>> EXPORT_SYMBOL(try_offline_node);
>>>>
>>>> -static int __ref try_remove_memory(u64 start, u64 size)
>>>> +static void __ref __try_remove_memory(int nid, u64 start, u64 size,
>>>> + struct vmem_altmap *altmap)
>>>> {
>>>> - struct vmem_altmap mhp_altmap = {};
>>>> - struct vmem_altmap *altmap = NULL;
>>>> - unsigned long nr_vmemmap_pages;
>>>> - int rc = 0, nid = NUMA_NO_NODE;
>>>> + /* remove memmap entry */
>>>> + firmware_map_remove(start, start + size, "System RAM");
>>>
>>> If mhp_supports_memmap_on_memory(), we will call
>>> firmware_map_add_hotplug() for whole range. But here we may call
>>> firmware_map_remove() for part of range. Is it OK?
>>>
>>
>> Good point, this is a discrepancy in the add vs remove path. Can the
>> firmware memmap entries be moved up a bit in the add path, and is it
>> okay to create these for each memblock? Or should these be for the
>> whole range? I'm not familiar with the implications. (I've left it as
>> is for v3 for now, but depending on the direction I can update in a
>> future rev).
>
> Cced more firmware map developers and maintainers.
>
> Per my understanding, we should create one firmware memmap entry for
> each memblock.

Ideally we should create it for the whole range, ti limit the ranges.
But it really only matters for DIMMs; for dax/kmem, we'll not create any
firmware entries.

--
Cheers,

David / dhildenb