Oct 12, 2025

WRT mmap paging, we are still seeing the same problem that we were formerly seeing on Linux, so macOS is not high performance presently (and Linux requires some simple config). The above change rules out sparse allocation as the issue. More likely just restrictive OS behavior that (unlike Linux) is not configurable. Windows dynamically manages this behavior, being optimal without any configuration required. Grok describes it as follows:

The problem isn't allocation—it's mmap itself on macOS for large files (>1GB per mapping, especially on APFS). Windows (SetEndOfFile / CreateFileMappingW) and Linux (mmap with native fallocate) handle large shared mappings reliably, but macOS has a long-standing kernel bug/limitation causing mmap failures or hangs for large files, even with preallocation. Here's the breakdown and fixes.