Function page_locality 

pub fn page_locality(
    entries: &[NumaMapsEntry],
    expected_nodes: &BTreeSet<usize>,
) -> f64

Compute page locality fraction from parsed numa_maps entries.

Returns the fraction of pages residing on any node in expected_nodes (0.0-1.0). Returns 0.0 when no pages are observed — a zero-allocation workload is not vacuously local; reporting 1.0 would let min_page_locality thresholds silently pass on broken runs that produced no NUMA signal. The expected node set is the cgroup’s cpuset NUMA-node set (the nodes whose CPUs the worker is confined to), supplied by the caller — see assert_cgroup in crate::assert::plan / crate::assert::reductions, not the worker’s MemPolicy.