Re: [LSF/MM/BPF TOPIC] 64k (or 16k) base page size on x86

[Dave Hansen]

On 2/23/26 03:27, David Hildenbrand (Arm) wrote:
...
>> BTW, x86-64 SysV ABI allows for 64k page size:
>>
>>     Systems are permitted to use any power-of-two page size between
>>     4KB and 64KB, inclusive.
>>
>> But it doesn't work in practice.
> 
> Even in well controlled environments you would run in a hyperscaler?

I think what Kirill is trying to say is that "it breaks userspace". ;)

A hyperscaler (or other "embedded" environment) might be willing or able
to go fix up userspace breakage. I would suspect our high frequency
trading friends would be all over this if it shaved a microsecond off
their receive times.

The more important question is what it breaks and how badly it breaks
things. 5-level paging, for instance, broke some JITs that historically
used the new (>48) upper virtual address bits for metadata. The gains
from 5-level paging were big enough and the userspace breakage was
confined and fixable enough that 5-level paging was viable.

I'm not sure which side a larger base page side will fall on, though. Is
it going to be an out-of-tree hack that a few folks use, or will it be
more like 5-level paging and be good enough that it goes into mainline?