Progress report in Pen programming language

June 4th, 2022

@raviqqe

Agenda

• Progress report
  • Heap reuse in record updates
• Next plans

Progress report

Heap reuse in record updates

• Programs reuse memory blocks if record updates are performed on unique references.
• Part of the Perceus reference counting algorithm
• Limited to records with more than one field
  • One-field records are planned to be unboxed.
• Similar to Arc::make_mut() in Rust

type foo {
  bar number
  baz number
}

f = \(x foo) foo {
  # Reuse a memory block originally allocated for x if its reference is unique.
  foo{...x, bar: 42}
}

Benchmark

• Map insertion
• Element count: 100,000
• ~20% improvement in time

Before:

> time ./app
./app  0.84s user 0.05s system 94% cpu 0.945 total

> valgrind ./app
total heap usage: 2,414,147 allocs, 2,414,074 frees, 262,931,512 bytes allocated

After:

> time ./app
./app  1.09s user 0.03s system 95% cpu 1.168 total

> valgrind ./app
total heap usage: 2,446,293 allocs, 2,446,220 frees, 279,647,432 bytes allocated

Further improvements

• Still so many allocations in the benchmark...
• Pen is missing some basic optimization.
  • e.g. lambda lifting

Others

• The standard Sql package
• FFI improvements
  • Conversion between lists in Pen and async streams in Rust
  • Type casting of any type values
• Attribute changes in LLVM
  • e.g. unnamed_addr, nounwind, etc.

Next plans

• Reference counting optimization
  • Relaxed atomic reference counting with sync bit #468
  • Unboxing small records #671
• Proper C calling convention in FFI #444
  • Compiling to MLIR?

Summary

• Progress
  • Heap reuse in record updates
• Next plans
  • Relaxed atomic reference counting
  • Record unboxing

Benchmark (old)

• Map insertion (with list iteration)
• Element count: 100,000

Before:

> time ./app
./app  0.94s user 0.08s system 95% cpu 1.064 total

> valgrind ./app
total heap usage: 3,414,149 allocs, 3,414,074 frees, 290,931,552 bytes allocated

After:

> time ./app
./app  1.10s user 0.05s system 95% cpu 1.202 total

> valgrind ./app
total heap usage: 3,446,295 allocs, 3,446,220 frees, 307,647,472 bytes allocated