From f1337566b9e27d06a890bf781a65994b2cbc073e Mon Sep 17 00:00:00 2001
From: Austin Seipp <aseipp@pobox.com>
Date: Wed, 1 Nov 2023 22:48:48 -0500
Subject: [PATCH] lib: memory optimization of `RepoPathComponent`

Summary: As suggested by Yuya. This is actually a huge win in heap allocations
for repositories with a lot of files; according to the bucket statistics from
mimalloc, on gecko-dev, a repo of ~350,000 files, this reduces the number of
small alloctions (8, 16, or 32 byte size class) from nearly ~4 million to just
over ~200k, a 20x allocation reduction, with a total peak heap size reduction of
over 50MiB.

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Change-Id: I4014145d740367ecec5be32c6b9e2de8
---
 Cargo.lock              | 35 +++++++++++++++++++++++++++++++++++
 Cargo.toml              |  1 +
 lib/Cargo.toml          |  1 +
 lib/src/content_hash.rs |  6 ++++++
 lib/src/repo_path.rs    | 11 +++++++----
 5 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 8ca6cf9ee1..298885ed1a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -302,6 +302,15 @@ version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "37b2a672a2cb129a2e41c10b1224bb368f9f37a2b16b612598138befd7b37eb5"
 
+[[package]]
+name = "castaway"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8a17ed5635fc8536268e5d4de1e22e81ac34419e5f052d4d51f4e01dcc263fcc"
+dependencies = [
+ "rustversion",
+]
+
 [[package]]
 name = "cc"
 version = "1.0.83"
@@ -429,6 +438,19 @@ version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "acbf1af155f9b9ef647e42cdc158db4b64a1b61f743629225fde6f3e0be2a7c7"
 
+[[package]]
+name = "compact_str"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f86b9c4c00838774a6d902ef931eff7470720c51d90c2e32cfe15dc304737b3f"
+dependencies = [
+ "castaway",
+ "cfg-if",
+ "itoa",
+ "ryu",
+ "static_assertions",
+]
+
 [[package]]
 name = "config"
 version = "0.13.3"
@@ -1667,6 +1689,7 @@ dependencies = [
  "byteorder",
  "bytes 1.5.0",
  "chrono",
+ "compact_str",
  "config",
  "criterion",
  "digest",
@@ -2485,6 +2508,12 @@ dependencies = [
  "windows-sys 0.48.0",
 ]
 
+[[package]]
+name = "rustversion"
+version = "1.0.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7ffc183a10b4478d04cbbbfc96d0873219d962dd5accaff2ffbd4ceb7df837f4"
+
 [[package]]
 name = "ryu"
 version = "1.0.15"
@@ -2678,6 +2707,12 @@ dependencies = [
  "windows-sys 0.48.0",
 ]
 
+[[package]]
+name = "static_assertions"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
+
 [[package]]
 name = "strsim"
 version = "0.10.0"
diff --git a/Cargo.toml b/Cargo.toml
index 93faa0a551..d8079000da 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -35,6 +35,7 @@ chrono = { version = "0.4.31", default-features = false, features = [
     "clock",
 ] }
 config = { version = "0.13.2", default-features = false, features = ["toml"] }
+compact_str = "0.7.1"
 criterion = "0.5.1"
 crossterm = { version = "0.26", default-features = false }
 digest = "0.10.7"
diff --git a/lib/Cargo.toml b/lib/Cargo.toml
index 03e979f920..4c5ccd9689 100644
--- a/lib/Cargo.toml
+++ b/lib/Cargo.toml
@@ -26,6 +26,7 @@ byteorder = { workspace = true }
 bytes = { workspace = true }
 chrono = { workspace = true }
 config = { workspace = true }
+compact_str = { workspace = true }
 digest = { workspace = true }
 futures = { workspace = true }
 either = { workspace = true }
diff --git a/lib/src/content_hash.rs b/lib/src/content_hash.rs
index 8f5d67a3a7..56035224dd 100644
--- a/lib/src/content_hash.rs
+++ b/lib/src/content_hash.rs
@@ -73,6 +73,12 @@ impl ContentHash for String {
     }
 }
 
+impl ContentHash for compact_str::CompactString {
+    fn hash(&self, state: &mut impl digest::Update) {
+        self.as_bytes().hash(state);
+    }
+}
+
 impl<T: ContentHash> ContentHash for Option<T> {
     fn hash(&self, state: &mut impl digest::Update) {
         match self {
diff --git a/lib/src/repo_path.rs b/lib/src/repo_path.rs
index d3ae6addaa..c755b1441f 100644
--- a/lib/src/repo_path.rs
+++ b/lib/src/repo_path.rs
@@ -17,6 +17,7 @@
 use std::fmt::{Debug, Error, Formatter};
 use std::path::{Component, Path, PathBuf};
 
+use compact_str::CompactString;
 use itertools::Itertools;
 use thiserror::Error;
 
@@ -25,7 +26,7 @@ use crate::file_util;
 content_hash! {
     #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
     pub struct RepoPathComponent {
-        value: String,
+        value: CompactString,
     }
 }
 
@@ -48,7 +49,9 @@ impl From<&str> for RepoPathComponent {
 impl From<String> for RepoPathComponent {
     fn from(value: String) -> Self {
         assert!(!value.contains('/'));
-        RepoPathComponent { value }
+        RepoPathComponent {
+            value: value.into(),
+        }
     }
 }
 
@@ -76,7 +79,7 @@ impl RepoPath {
             let components = value
                 .split('/')
                 .map(|value| RepoPathComponent {
-                    value: value.to_string(),
+                    value: value.into(),
                 })
                 .collect();
             RepoPath { components }
@@ -141,7 +144,7 @@ impl RepoPath {
         let repo_path_len: usize = self.components.iter().map(|x| x.as_str().len() + 1).sum();
         let mut result = PathBuf::with_capacity(base.as_os_str().len() + repo_path_len);
         result.push(base);
-        result.extend(self.components.iter().map(|dir| &dir.value));
+        result.extend(self.components.iter().map(|dir| dir.value.as_str()));
         result
     }