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aarch64 48-bit Virtual Address Space

Before Fedora 26, the aarch64 kernel in Fedora used a 42-bit process virtual address (VA) space and due to the way aarch64 paging works, this constrained the maximum physical address as well. The 42-bit VA was fairly limiting for some applications, but aarch64 processors also have support for 48-bit VAs.

For Fedora 26, Fedora has introduced a 48-bit VA and so larger aarch64 processes won’t be constrained by the virtual or physical limitations of a 42-bit VA. This change also helps with things like hugetlb’s and potentially provides a performace boost. Additionally, it allows Fedora to boot on a class of machines that have the majority of their RAM higher in the address space.

Its unlikely a desktop user will notice the change, except possibly that Fedora might now boot on additional hardware. A server user might find that there is more RAM available for in-memory databases etc.