Lib.rs

› Memory management
#alloc #benchmark #stats-alloc

stats_alloc_helper

A test helper to measure memory allocations

by Ivan Babrou

4 releases (2 breaking)

0.3.1 Oct 6, 2024
0.3.0 Oct 1, 2024
0.2.0 Sep 30, 2024
0.1.0 Sep 29, 2024

#87 in Memory management

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BSD-3-Clause

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stats_alloc_helper

A crate that provides a helper to measure memory allocations in tests.

Example

To allow measuring allocations, you must use the provided LockedAllocator, because otherwise tests running in other thread could mess up the numbers.

Synchronous code

Typically this means a setup similar to the following in tests:

use std::alloc::System;
use stats_alloc::{StatsAlloc, Stats};
use stats_alloc_helper::{LockedAllocator, memory_measured};

#[global_allocator]
static GLOBAL: LockedAllocator<System> = LockedAllocator::new(StatsAlloc::system());

// In the actual tests:

let mut length = 0;

let stats = memory_measured(&GLOBAL, || {
    let s = "whoa".to_owned().replace("whoa", "wow").to_owned();

    length = s.len();
});

assert_eq!(length, 3);

assert_eq!(
    stats,
    Stats {
        allocations: 3,
        deallocations: 3,
        reallocations: 0,
        bytes_allocated: 15,
        bytes_deallocated: 15,
        bytes_reallocated: 0
    }
);

Async code

Async futures are supported with async_tokio feature enabled:

#[tokio::test]
async fn test_tokio() {
    let stats = memory_measured_future(&GLOBAL, async {
        let _ = vec![1, 2, 3, 4];
    })
    .await;

    assert_eq!(
        stats,
        Stats {
            allocations: 1,
            deallocations: 1,
            reallocations: 0,
            bytes_allocated: 16,
            bytes_deallocated: 16,
            bytes_reallocated: 0
        }
    );
}

This is achieved by creating a separate single threaded runtime on a separate thread and driving the future to completion on it.

Keep in mind that your future must be able to be driven to completion on a separate runtime with no dependencies on the main one.

If you create a complex client on the main runtime (think hyper) and try to test one method of it on a separate runtime, you might discover a deadlock because there's a background future being driven by the main runtime that is blocked trying to access a locked allocator.

You can solve this by:

  1. Measure how much memory it takes to create a client.
  2. Measure how much memory it takes to create a client and do a thing.
  3. Subtract the former from the latter.

USDT probes and flamegraphs

This crates adds USDT probes for locked allocations as well:

  • LockedAllocator:alloc_locked
  • LockedAllocator:dealloc_locked
  • LockedAllocator:realloc_locked

To see allocations from a particular test, one can use perf:

  1. Compile the tests and note the binary produced:
$ cargo test --no-run
   Compiling stats_alloc_helper v0.3.0 (/home/ivan/projects/stats_alloc_helper)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 5.09s
  Executable unittests src/lib.rs (target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
  1. Add the probes for allocations for the binary above:
$ sudo perf probe -x ./target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4 --add sdt_LockedAllocator:alloc_locked
Added new event:
  sdt_LockedAllocator:alloc_locked (on %alloc_locked in /home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)

You can now use it in all perf tools, such as:

	perf record -e sdt_LockedAllocator:alloc_locked -aR sleep 1
  1. Start collecting the data with perf in one terminal:
$ sudo perf record -a -e sdt_LockedAllocator:alloc_locked -g --call-graph dwarf
  1. Run the tests in another terminal:
$ ./target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4 -- --tests it_works

running 1 test
test tests::it_works ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 1 filtered out; finished in 0.01s
  1. Stop perf with ctrl+c and run perf script to view events:
$ sudo perf script
tests::it_works    7342 [002]  1331.303361: sdt_LockedAllocator:alloc_locked: (556e86e548)
	      556e86e548 _$LT$stats_alloc_helper..LockedAllocator$LT$T$GT$$u20$as$u20$core..alloc..global..GlobalAlloc$GT$::alloc::_$u7b$$u7b$closure$u7d$$u7d$::h6f705db76a45b45d+0x3c (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e86e2bb stats_alloc_helper::LockedAllocator<T>::serialized+0x7b (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e86e4ff <stats_alloc_helper::LockedAllocator<T> as core::alloc::global::GlobalAlloc>::alloc+0x33 (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e865f6f __rust_alloc+0x2b (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e865763 alloc::alloc::alloc+0x6f (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e86586f alloc::alloc::Global::alloc_impl+0xff (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e865f37 <alloc::alloc::Global as core::alloc::Allocator>::allocate+0x23 (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e86dc7b alloc::raw_vec::RawVec<T,A>::try_allocate_in+0x183 (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e868e27 alloc::raw_vec::RawVec<T,A>::with_capacity_in+0x3b (inlined)
	      556e868e27 alloc::vec::Vec<T,A>::with_capacity_in+0x3b (inlined)
	      556e868e27 <T as alloc::slice::hack::ConvertVec>::to_vec+0x3b (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e86496b alloc::slice::hack::to_vec+0x2b (inlined)
	      556e86496b alloc::slice::<impl [T]>::to_vec_in+0x2b (inlined)
	      556e86496b alloc::slice::<impl [T]>::to_vec+0x2b (inlined)
	      556e86496b alloc::slice::<impl alloc::borrow::ToOwned for [T]>::to_owned+0x2b (inlined)
	      556e86496b alloc::str::<impl alloc::borrow::ToOwned for str>::to_owned+0x2b (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e86f9cb stats_alloc_helper::tests::it_works::_$u7b$$u7b$closure$u7d$$u7d$::h064bc6e2ead5ac9c+0x27 (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e86e7eb stats_alloc_helper::memory_measured+0x6b (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e866083 stats_alloc_helper::tests::it_works+0x2b (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e86f98f stats_alloc_helper::tests::it_works::_$u7b$$u7b$closure$u7d$$u7d$::hb3e72c754a919576+0x13 (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e8665c3 core::ops::function::FnOnce::call_once+0xf (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e89d54b core::ops::function::FnOnce::call_once+0x13 (inlined)
	      556e89d54b test::__rust_begin_short_backtrace+0x13 (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e89cdfb test::run_test_in_process::_$u7b$$u7b$closure$u7d$$u7d$::h890e037ea78eb892+0x14f (inlined)
	      556e89cdfb <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once+0x14f (inlined)
	      556e89cdfb std::panicking::try::do_call+0x14f (inlined)
	      556e89cdfb std::panicking::try+0x14f (inlined)
	      556e89cdfb std::panic::catch_unwind+0x14f (inlined)
	      556e89cdfb test::run_test_in_process+0x14f (inlined)
	      556e89cdfb test::run_test::_$u7b$$u7b$closure$u7d$$u7d$::hd93cbd5460493157+0x14f (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e870057 test::run_test::_$u7b$$u7b$closure$u7d$$u7d$::h3980614fdc2390bb+0x93 (inlined)
	      556e870057 std::sys_common::backtrace::__rust_begin_short_backtrace+0x93 (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e8745db std::thread::Builder::spawn_unchecked_::_$u7b$$u7b$closure$u7d$$u7d$::_$u7b$$u7b$closure$u7d$$u7d$::h8a21f0157e97fbf6+0x8f (inlined)
	      556e8745db <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once+0x8f (inlined)
	      556e8745db std::panicking::try::do_call+0x8f (inlined)
	      556e8745db std::panicking::try+0x8f (inlined)
	      556e8745db std::panic::catch_unwind+0x8f (inlined)
	      556e8745db std::thread::Builder::spawn_unchecked_::_$u7b$$u7b$closure$u7d$$u7d$::h50d9109153134c66+0x8f (inlined)
	      556e8745db core::ops::function::FnOnce::call_once$u7b$$u7b$vtable.shim$u7d$$u7d$::hd9dcdfc921101872+0x8f (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      556e8c69e7 <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once+0x2b (inlined)
	      556e8c69e7 <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once+0x2b (inlined)
	      556e8c69e7 std::sys::pal::unix::thread::Thread::new::thread_start+0x2b (/home/ivan/projects/stats_alloc_helper/target/debug/deps/stats_alloc_helper-9847447b1d1ec0c4)
	      7fab6efe83 start_thread+0x383 (/usr/lib/aarch64-linux-gnu/libc.so.6)
	      7fab6efe83 start_thread+0x383 (/usr/lib/aarch64-linux-gnu/libc.so.6)

...
  1. With a bit of ingenuity, you can turn this into a flamegraph:
sudo perf script | sed 's/sdt_LockedAllocator:.*//' | inferno-collapse-perf | inferno-flamegraph --truncate-text-right > flamegraph.svg

See flamegraph.svg in the repo

Dependencies

~0–6MB
~23K SLoC