GoKawiilBenchmarks show musl libc lags glibc by up to 26% even with mimalloc swapped in
A developer investigating containerized Rust performance found that musl's default memory allocator is significantly slower than glibc's, not just under high concurrency but even on modest 4-core EC2 instances. Swapping in mimalloc or jemalloc narrows the gap but doesn't close it—one workload remained 26% slower—because several of musl's core memory routines are themselves inefficient, not just its allocator.
GoKawiil's interpretation of the reporting above, not reported fact.
Many developers choose musl for Rust and other statically-linked binaries assuming it's a drop-in, lightweight alternative to glibc with no real downside. This research shows that assumption can silently tank performance in production, especially for allocation-heavy workloads, making musl a riskier default than commonly believed.
- musl's built-in allocator underperforms glibc's even outside high-concurrency scenarios.
- Installing mimalloc or jemalloc helps but doesn't fully close the performance gap—up to 26% slower persisted in tests.
- Slow memory routines beyond the allocator itself are also to blame, prompting the author to drop musl from performance-sensitive projects.
Programming Rust, 2nd Edition (O'Reilly) — If you're wrestling with Rust builds, static linking targets and allocator choices like the author, this O'Reilly guide is the deep reference that explains how Rust manages memory and links against system libraries. It's the kind of book you keep open while debugging why your musl container binary behaves differently than glibc.
See Programming Rust, 2nd Edition (O'Reilly) on Amazon → Affiliate link — we may earn a commission on purchases, at no extra cost to you. Product picked by AI based on this article; it is not a tested recommendation.Source: blog.brokk.ai, 2026-08-28
Published there as: “Don't use musl if you care about performance”
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