Runtime code modification used by static keys is the most ubiquitous
self-modifying feature of the Linux kernel. The idea is to to eliminate
the condition check and associated conditional jump on a hot path if
that condition (based on a boolean value of a static key) does not
change often. Whenever they condition changes, the kernel runtime
modifies all code paths associated with that key flipping the code
between nop and (unconditional) jump.
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