diff --git a/_drafts/case-study-optimization.md b/_drafts/case-study-optimization.md index 0437cc1..bf97d8a 100644 --- a/_drafts/case-study-optimization.md +++ b/_drafts/case-study-optimization.md @@ -1,7 +1,7 @@ --- layout: post title: "A Case Study in Heaptrack" -description: "...because you don't need no garbage collection " +description: "...because you don't need no garbage collection" category: tags: [] --- @@ -17,15 +17,15 @@ One of my earliest conversations about programming went like this: [graphing calculator](https://education.ti.com/en/products/calculators/graphing-calculators/ti-84-plus-se) packing a whole 24KB of RAM. By the way, *what are you doing on my lawn?* -The principle remains though: be efficient with the resources you're given, because +The principle remains though: be efficient with the resources you have, because [what Intel giveth, Microsoft taketh away](http://exo-blog.blogspot.com/2007/09/what-intel-giveth-microsoft-taketh-away.html). My professional work is focused on this kind of efficiency; low-latency financial markets demand that you understand at a deep level *exactly* what your code is doing. As I continue experimenting with Rust for personal projects, it's exciting to bring a utilitarian mindset with me: there's flexibility for the times I pretend -to have a garbage collector, and flexibility for the times that I really care about efficiency. +to have a garbage collector, and flexibility for the times that I really care about how memory is used. -This post is a (small) case study in how I went from the former to the latter. And it's an attempt to prove how easy -it is for you to do the same. +This post is a (small) case study in how I went from the former to the latter. And ultimately, it's intended +to be a starting toolkit to empower analysis of your own code. # Curiosity @@ -33,7 +33,7 @@ When I first started building the [dtparse] crate, my intention was to mirror as the equivalent [Python library][dateutil]. Python, as you may know, is garbage collected. Very rarely is memory usage considered in Python, and I likewise wasn't paying too much attention when `dtparse` was first being built. -That works out well enough, and I'm not planning on making that `dtparse` hyper-efficient. +This lackadaisical approach to memory works well enough, and I'm not planning on making `dtparse` hyper-efficient. But every so often, I've wondered: "what exactly is going on in memory?" With the advent of Rust 1.28 and the [Global Allocator trait](https://doc.rust-lang.org/std/alloc/trait.GlobalAlloc.html), I had a really great idea: *build a custom allocator that allows you to track your own allocations.* That way, you can do things like @@ -47,10 +47,10 @@ Instead, I'll highlight a separate path I took to make sense of my memory usage: This is the hardest part of the post. Because Rust uses [its own allocator](https://github.com/rust-lang/rust/pull/27400#issue-41256384) by default, -`heaptrack` is unable to properly record what your code is doing out of the box. Instead, -we compile our programs with some special options to make it work. +`heaptrack` is unable to properly record unmodified Rust code. To remedy this, we'll make use +of the `#[global_allocator]` attribute. -Specifically, in `lib.rs` or `main.rs`, make sure you add this: +Specifically, in `lib.rs` or `main.rs`, add this: ```rust use std::alloc::System; @@ -86,8 +86,8 @@ And even these pretty colors: To make sense of our memory usage, we're going to focus on that last picture - it's called a ["flamegraph"](http://www.brendangregg.com/flamegraphs.html). These charts are typically -used to show how much time you spend executing different functions, but they're used here -to show how much memory was allocated during those functions. +used to show how much time your program spends executing each function, but they're used here +to show how much memory was allocated during those functions instead. For example, we can see that all executions happened during the `main` function: @@ -128,9 +128,9 @@ pub fn parse(timestr: &str) -> ParseResult<(NaiveDateTime, Option)> --- -Because `Parser::parse` requires a mutable reference to itself, I have to create a new parser -every time it receives a string. This seems excessive! We'd rather have an immutable parser -that can be re-used, and avoid needing to allocate memory in the first place. +Because `Parser::parse` requires a mutable reference to itself, I have to create a new `Parser::default` +every time it receives a string. This is excessive! We'd rather have an immutable parser +that can be re-used, and avoid allocating memory in the first place. Armed with that information, I put some time in to [make the parser immutable](https://github.com/bspeice/dtparse/commit/741afa34517d6bc1155713bbc5d66905fea13fad#diff-b4aea3e418ccdb71239b96952d9cddb6). @@ -138,11 +138,11 @@ Now that I can re-use the same parser over and over, the allocations disappear: ![allocations cleaned up](/assets/images/2018-10-heaptrack/heaptrack-flamegraph-after.png) -In total, we went from requiring 2 MB of memory: +In total, we went from requiring 2 MB of memory in [version 1.0.2](https://crates.io/crates/dtparse/1.0.2): ![memory before](/assets/images/2018-10-heaptrack/heaptrack-closeup.png) -All the way down to 300KB: +All the way down to 300KB in [version 1.0.3](https://crates.io/crates/dtparse/1.0.3): ![memory after](/assets/images/2018-10-heaptrack/heaptrack-closeup-after.png)