Four instrumented real-repo bench runs scored 0 cache hits: libgit2's
mwindow layer reuses its open windows, so only genuinely new
(offset, len) ranges ever reach p_mmap — there is no repetition to
cache. The 7.4 MB OOM the v2 discipline fixed was caused by the cache
itself holding buffers past p_munmap; plain free-at-munmap is honest
with MWINDOW_MAPPED_LIMIT by construction. Run 5 confirmed removal is
I/O-neutral on device (byte-identical read pattern, warm splice 1953
vs 1949 ms) and even 15 reads better — v2's low-water eviction was
fighting mwindow. Stats counters kept to spot any future workload
that does repeat ranges.
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