Optimize Release Builds for Size and Speed

Intermediate10 min

Tune Cargo release profiles to produce smaller, faster binaries using LTO, codegen units, and stripping.

Prerequisites

-Rust toolchain installed
-A Cargo project

Steps

Configure release profile in Cargo.toml

Add optimization settings to the release profile for smaller and faster builds.

$ cat >> Cargo.toml << 'EOF' [profile.release] opt-level = 3 lto = true codegen-units = 1 panic = "abort" strip = true EOF

codegen-units = 1 produces better optimized code but increases compile time.

Build the optimized release binary

Compile with the release profile to apply all optimizations.

$ cargo build --release

Compare debug vs release binary size

Check the size difference between debug and release builds.

$ cargo build 2>/dev/null && cargo build --release 2>/dev/null && ls -lh target/debug/myapp target/release/myapp

Optimize for size instead of speed

Use opt-level 's' or 'z' when binary size matters more than raw speed.

$ cat > Cargo.toml.size-opt << 'EOF' [profile.release] opt-level = "z" lto = true codegen-units = 1 panic = "abort" strip = true EOF echo 'Append the above to Cargo.toml for size-optimized builds'

opt-level 'z' optimizes aggressively for size. 's' is a balance between size and speed.

Analyze binary size with cargo-bloat

Find which functions and crates contribute most to the binary size.

$ cargo install cargo-bloat && cargo bloat --release -n 20

Full Script

full-script.sh

#!/bin/bash
# Rust Release Optimization
set -euo pipefail

echo "=== Debug Build ==="
cargo build 2>&1 | tail -1
DEBUG_SIZE=$(stat -f%z target/debug/myapp 2>/dev/null || stat -c%s target/debug/myapp 2>/dev/null || echo "0")

echo ""
echo "=== Release Build ==="
cargo build --release 2>&1 | tail -1
RELEASE_SIZE=$(stat -f%z target/release/myapp 2>/dev/null || stat -c%s target/release/myapp 2>/dev/null || echo "0")

echo ""
echo "=== Size Comparison ==="
echo "Debug:   $(numfmt --to=iec $DEBUG_SIZE 2>/dev/null || echo "${DEBUG_SIZE} bytes")"
echo "Release: $(numfmt --to=iec $RELEASE_SIZE 2>/dev/null || echo "${RELEASE_SIZE} bytes")"

echo ""
echo "=== Optimization Profile ==="
echo "[profile.release]"
echo "opt-level = 3        # Max speed (use 'z' for min size)"
echo "lto = true           # Link-time optimization"
echo "codegen-units = 1    # Better optimization, slower compile"
echo "panic = "abort"      # Smaller binary, no unwinding"
echo "strip = true         # Remove debug symbols"

FAQ

Discussion

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#!/bin/bash # Rust Release Optimization set -euo pipefail echo "=== Debug Build ===" cargo build 2>&1 | tail -1 DEBUG_SIZE=$(stat -f%z target/debug/myapp 2>/dev/null || stat -c%s target/debug/myapp 2>/dev/null || echo "0") echo "" echo "=== Release Build ===" cargo build --release 2>&1 | tail -1 RELEASE_SIZE=$(stat -f%z target/release/myapp 2>/dev/null || stat -c%s target/release/myapp 2>/dev/null || echo "0") echo "" echo "=== Size Comparison ===" echo "Debug: $(numfmt --to=iec $DEBUG_SIZE 2>/dev/null || echo "${DEBUG_SIZE} bytes")" echo "Release: $(numfmt --to=iec $RELEASE_SIZE 2>/dev/null || echo "${RELEASE_SIZE} bytes")" echo "" echo "=== Optimization Profile ===" echo "[profile.release]" echo "opt-level = 3 # Max speed (use 'z' for min size)" echo "lto = true # Link-time optimization" echo "codegen-units = 1 # Better optimization, slower compile" echo "panic = "abort" # Smaller binary, no unwinding" echo "strip = true # Remove debug symbols"