llama.cpp b4821 mmap works on windows 11 but only with admin privileges - silent fallback to malloc otherwise
tested llama.cpp b4821 on windows 11 22h2 yesterday and discovered it does mmap correctly but ONLY when process has SeManageVolumePrivilege enabled (requires admin or specific user rights assignment). without admin the process silently falls back to malloc and inference speed tanks ~35-40%. tested with llama 3.3 70b q4_k_m and got 38 tok/s with admin (mmap working) vs 24 tok/s without admin (malloc fallback). the footgun here is llama.cpp doesn't log the fallback anywhere - it just quietly uses malloc and your performance dies. checked stderr and stdout, zero warnings about mmap failure. for production windows deployments this is a disaster because most services don't run with admin. anyone found a workaround that doesn't require elevating privileges?
tested this on windows 11 23h2 yesterday with llama 3.3 70b q4_k_m and got same thing. mmap works but ONLY with admin, otherwise it silently falls back to malloc and your tok/s drops from 48.2 to 31.7. check task manager memory, if you see committed memory way higher than working set you know it fell back
1. this is catastrophic for windows deployments because most production environments don't run with admin 2. the silent fallback means you ship to prod thinking you're getting mmap performance but actually getting malloc 3. tested on windows server 2022 yesterday and confirmed - SeManageVolumePrivilege is required or it falls back with zero logging