MemoryStore now uses fixed memory pool per store

MemoryStore now pre-allocates max_bytes from the eviction policy,
then installs a custom allocator in that pool that the store will
use. In testing, memory fragmentation appears to have dropped
significantly, significantly decreased the number of sys-calls
managing memory and slightly reduced user time.

In addition, we remove two full copies of our data when we store
it in the memory store.

This PR also adds two new crates (likely to be published).

"Heap Allocator"
  Fixed heap allocator based on the TLSF (Two-Level Segregated
  Fit) algorithm. TLSF is a fast, constant-time memory allocation
  algorithm designed for real-time applications. It organizes free
  memory into segregated lists based on block sizes, allowing for
  quick allocation and deallocation with minimal fragmentation.

"Alloc Bytes"
  Provides custom byte buffers allocated using a user-provided
  allocator. It offers both mutable and immutable byte buffers,
  enabling efficient memory allocation strategies in systems with
  custom memory requirements.

closes: #289

Author: allada

Cargo.lock

@@ -46,6 +46,8 @@ nativelink-util = { path = "nativelink-util" }
 nativelink-worker = { path = "nativelink-worker" }
 nativelink-metric = { path = "nativelink-metric" }
 nativelink-metric-collector = { path = "nativelink-metric-collector" }
+alloc-bytes = { path = "external-crates/alloc-bytes" }
+heap-allocator = { path = "external-crates/heap-allocator" }
 async-lock = { version = "3.4.0", features = ["std"], default-features = false }
 axum = { version = "0.7.9", default-features = false }
 clap = { version = "4.5.26", features = ["derive"] }

Cargo.toml

@@ -36,6 +36,8 @@ crate.from_cargo(
     cargo_lockfile = "//:Cargo.lock",
     manifests = [
         "//:Cargo.toml",
+        "//external-crates/alloc-bytes:Cargo.toml",
+        "//external-crates/heap-allocator:Cargo.toml",
         "//nativelink-config:Cargo.toml",
         "//nativelink-error:Cargo.toml",
         "//nativelink-macro:Cargo.toml",

MODULE.bazel

@@ -0,0 +1,31 @@
+load(
+    "@rules_rust//rust:defs.bzl",
+    "rust_doc",
+    "rust_doc_test",
+    "rust_library",
+)
+
+rust_library(
+    name = "alloc-bytes",
+    srcs = [
+        "src/lib.rs",
+    ],
+    crate_features = ["bytes"],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//external-crates/heap-allocator",
+        "@crates//:bytes",
+    ],
+)
+
+rust_doc(
+    name = "docs",
+    crate = ":alloc-bytes",
+    visibility = ["//visibility:public"],
+)
+
+rust_doc_test(
+    name = "doc_test",
+    timeout = "short",
+    crate = ":alloc-bytes",
+)

external-crates/alloc-bytes/BUILD.bazel

@@ -0,0 +1,25 @@
+[package]
+name = "alloc-bytes"
+version = "0.0.1"
+edition = "2018"
+authors = [
+  "Nativelink Authors",
+  "Nathan (Blaise) Bruer <[email protected]>"
+]
+license = "Apache-2.0"
+repository = "https://github.com/TraceMachina/nativelink/external-crates/alloc-bytes"
+description = "A lightweight crate offering custom-allocated byte buffers with user-specified allocators for efficient, fine-tuned memory management."
+keywords = ["bytes", "allocator", "buffers"]
+categories = ["network-programming", "data-structures"]
+
+[lib]
+crate-type = ["rlib"]
+
+[dependencies]
+bytes = { version = "1.10.0", optional = true, default-features = false }
+heap-allocator = { path = "../heap-allocator", optional = true }
+
+[features]
+default = []
+
+bytes = ["dep:bytes"]