Cracking the 250 KB Ceiling: How a Rust Wallpaper Daemon Slashes Runtime Memory

In the world of Linux desktop environments, wallpaper setting is a surprisingly heavy operation. Most Wayland compositors expose a shared‑memory protocol that requires a client to allocate a buffer, copy the image data into it, and then hand it off to the compositor. The resulting binaries typically weigh in at several megabytes of RAM, even when the image itself is tiny. The author of the post on lgfae.com set out to reverse that trend and demonstrate that a Rust daemon can keep its resident set size under 250 KB.

Source: https://www.lgfae.com/posts/2025-11-21-SettingAWallpaperWithLessThan250KB.html

The 230 KB Benchmark

The daemon’s idle footprint is 230 KB on a Linux machine, as shown in the ps output below. The figure is the PSS (proportional set size), which accounts for shared pages, giving a realistic view of the memory actually used by the process.

The key to this result is a two‑branch build: a no‑libc daemon that compiles with rustix and origin, and a client that runs with the standard library. The daemon itself never pulls in the heavy std or libc layers, and it avoids dynamic allocation wherever possible.

Custom Wayland Client

The author’s first optimization is a hand‑rolled Wayland protocol implementation, called waybackend. Unlike the smithay client toolkit or wayrs, which wrap the C libwayland-client API for ergonomics, waybackend implements the protocol directly in Rust. By storing Wayland objects as a single byte‑sized enum instead of the 16‑byte structures used by other libraries, the daemon saves dozens of bytes per object. The trade‑off is a higher learning curve: each request must be constructed by consulting the Wayland protocol spec, but the resulting code is dramatically leaner.

No‑Std, No‑Libc, No‑C

1. rustix for Syscalls

rustix provides thin wrappers over Linux syscalls that do not depend on libc. In a no‑std context, the author writes a minimal main that parses argc/argv manually and uses rustix::fs::open instead of std::fs::File. This eliminates the entire C runtime and the overhead of the standard library’s allocator.

2. origin for Startup

The origin crate supplies a custom _start symbol, environment variable handling, and signal‑safe startup code. Combined with rustix, it replaces the default libc startup sequence, freeing the daemon from glibc’s baggage.

3. talc Allocator

Memory allocation is the next bottleneck. The author replaces the default allocator with talc, which allows custom out‑of‑memory handling and can request more memory via mmap directly. This removes the allocator metadata overhead that typical allocators impose on each allocation.

Cutting Allocation Costs

Smallvec and German Strings

The daemon uses smallvec to keep small collections on the stack, avoiding heap allocations for the common case of a handful of monitors. For strings that never exceed 14 bytes (the maximum Wayland message size minus protocol overhead), the author implements a German string representation: a 4‑byte length field and a 12‑byte inline buffer. This eliminates the String’s heap pointer and capacity, saving 16 bytes per string.

Manual Rc/RefCell

Wallpaper objects were originally wrapped in Rc<RefCell<T>>, which adds 24 bytes of bookkeeping per object. By observing that strong counts never exceed three and that borrows are always unique, the author re‑implemented the reference counting with a single u8 and a boolean flag, inline with the wallpaper struct. The resulting savings are modest but meaningful when multiplied across dozens of objects.

Enum Variant Size Awareness

Clippy warns when an enum variant is an order of magnitude larger than the others. The author boxes such variants to keep the enum size tight, trading a single allocation for a smaller stack footprint.

Logging and Error Handling

The standard log crate’s macro API pulls in extra code for multiple log target formats. The daemon implements a lightweight logger that only supports the simplest format, eliminating unnecessary code and keeping the binary small.

For panics, a custom panic_handler prints the file, line, and column without allocating, then aborts. This is crucial because a panic‑path that allocates would trigger the out‑of‑memory handler and potentially double‑allocate.

Generics vs. Dynamic Dispatch

Rust’s monomorphization can inflate binary size when a generic function is instantiated for many types. The author limited the use of generics to cases where the type set is small, and used dynamic dispatch (dyn) only when the code path was exercised infrequently. This reduced the number of code copies in the final binary.

Practical Takeaways

  1. Strip the runtime – a no‑std, no‑libc build can cut memory by an order of magnitude.
  2. Lean protocol stacks – custom Wayland clients can avoid the overhead of ergonomic libraries.
  3. Allocation hygiene – use stack‑based containers and inline strings where possible.
  4. Measure, then iterate – tools like cargo-bloat, ps, and valgrind are indispensable for verifying gains.

These techniques are not limited to wallpaper daemons. Any long‑running daemon that needs to stay below a few megabytes of RAM—cron, system monitoring tools, or embedded services—can benefit from a similar approach.

Closing Thoughts

The post demonstrates that a careful, low‑level Rust program can achieve a runtime footprint comparable to hand‑written assembly, while still retaining the safety and expressiveness of Rust. For developers building on resource‑constrained Linux systems, the lesson is clear: every allocation matters, and a disciplined approach to memory can pay off in measurable performance and energy savings.

Image credit: awww‑daemon memory usage snapshot.