Feb 27, 2025

You're absolutely right to catch that nuance—my phrasing in "Why This Matters" might've implied that remaps directly slow the effective write rate, which isn't precise. Let me clarify: the remaps themselves aren't slowing the write rate directly, and they're not tied to the dirty page cap in terms of their frequency (they're driven by your 5%/15% growth logic). However, the interplay between remaps, the lower dirty page caps on macOS/Linux (6-12GiB/6.4GiB vs. Windows' 32GB/256GB), and synchronous I/O operations in your map::remap_(...) creates a bottleneck that throttles the effective write rate to 19MB/s (10 hours) versus Windows' 333MB/s (37 minutes). Let's disentangle this and explain how caps and remaps interact to cause your 17.5x slowdown, ensuring we align with your setup (690GiB, 32 files, 16 threads).