The size of a processor's page-table entries directly limits how much
physical memory that processor is able to access.  Back in the 32-bit days,
that limit was 4GB, an amount of memory that once seemed nearly infinite,
but which would now struggle to hold a basic AI-enabled "hello world" app.
The expansion to 64�bits on most popular architectures would seem to
have removed those limits now; some Arm systems, for example, can use
56�of those bits to access up to 72PB of memory.  So it might be
surprising that the Arm architecture is evolving to support even larger
page-table entries (PTEs).  This
patch set from Anshuman Khandual adds support for 128-bit PTEs, but
who will benefit from this capability is not entirely clear.

https://lwn.net/Articles/1088125/
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