Re: [PATCH] iommu/mediatek: Use totalram_pages to setup enable_4GB

[David Hildenbrand]

On 04.06.20 17:06, Christoph Hellwig wrote:
> On Thu, Jun 04, 2020 at 01:32:40PM +0200, David Hildenbrand wrote:
>> Just a thought: If memory hotplug is applicable as well, you might
>> either want to always assume data->enable_4GB, or handle memory hotplug
>> events from the memory notifier, when new memory gets onlined (not sure
>> how tricky that is).
> 
> We probably want a highest_pfn_possible() or similar API instead of
> having drivers poking into random VM internals.

Well, memory notifiers are a reasonable api used accross the kernel to
get notified when new memory is onlined to the buddy that could be used
for allocations.

highest_pfn_possible() would have to default to something linked to
MAX_PHYSMEM_BITS whenever memory hotplug is configured, I am not sure
how helpful that is (IOW, you can just default to enable_4GB=true in
that case instead in most cases).

-- 
Thanks,

David / dhildenb