custom-allocators

사용 방법

설치 명령을 복사하고 자신의 에이전트 환경에 설치하기 전에 소스 패키지를 확인하세요.
필요한 도구, 인증 정보, 지원 환경은 원본 문서에서 확인하세요.
입력과 원하는 산출물을 설명하고 출처와 결과를 대조하세요.

npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill custom-allocators

시작 전 확인

설치에는 모델 구독, API 한도, 파일 접근 권한이 포함되지 않습니다.
별점 수와 설치 수는 활동 지표이며 독립적인 품질·보안 검증이 아닙니다.

원본 Skill 문서

원본 저장소의 제목, 예시, 코드, 표, 링크, 이미지를 유지해 표시합니다.

Custom Allocators

Purpose

Guide agents through memory allocator design and tuning: pool/slab/arena/buddy taxonomy, jemalloc internals and MALLOC_CONF, mimalloc design, tcmalloc thread-caching, writing a simple pool allocator in C, Rust GlobalAlloc trait, fragmentation metrics, and benchmarking.

When to Use

Replacing malloc for latency-sensitive or embedded workloads
Tuning jemalloc/mimalloc for server heap behavior
Implementing arena allocation for request-scoped or frame-based lifetimes
Writing a Rust custom global allocator for no_std or performance
Diagnosing heap fragmentation (internal vs external)
Benchmarking allocator throughput and latency

Workflow

1. Allocator taxonomy

Allocator types
├── Pool/fixed-size — O(1) alloc/free, fixed block sizes
├── Slab — kernel-style, cache-friendly size classes
├── Arena/bump — fast alloc, bulk free (reset arena)
├── Buddy — power-of-two blocks, low fragmentation for large allocs
└── General (malloc) — jemalloc, mimalloc, tcmalloc

2. Simple pool allocator in C

#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>

typedef struct pool_block {
    struct pool_block *next;
} pool_block_t;

typedef struct {
    void   *memory;
    size_t  block_size;
    size_t  num_blocks;
    pool_block_t *free_list;
} pool_t;

int pool_init(pool_t *p, size_t block_size, size_t num_blocks) {
    p->block_size = block_size < sizeof(pool_block_t) ?
        sizeof(pool_block_t) : block_size;
    p->num_blocks = num_blocks;
    p->memory = aligned_alloc(64, p->block_size * num_blocks);
    if (!p->memory) return -1;
    p->free_list = NULL;
    for (size_t i = 0; i < num_blocks; i++) {
        pool_block_t *blk = (pool_block_t *)((char *)p->memory + i * p->block_size);
        blk->next = p->free_list;
        p->free_list = blk;
    }
    return 0;
}

void *pool_alloc(pool_t *p) {
    if (!p->free_list) return NULL;
    pool_block_t *blk = p->free_list;
    p->free_list = blk->next;
    return blk;
}

void pool_free(pool_t *p, void *ptr) {
    pool_block_t *blk = (pool_block_t *)ptr;
    blk->next = p->free_list;
    p->free_list = blk;
}

3. Arena allocator

typedef struct {
    char  *base;
    size_t capacity;
    size_t offset;
} arena_t;

void *arena_alloc(arena_t *a, size_t size, size_t align) {
    uintptr_t cur = (uintptr_t)(a->base + a->offset);
    uintptr_t aligned = (cur + align - 1) & ~(align - 1);
    size_t padding = aligned - cur;
    if (a->offset + padding + size > a->capacity)
        return NULL;
    a->offset += padding + size;
    return (void *)aligned;
}

void arena_reset(arena_t *a) { a->offset = 0; }

Use per-request arenas in servers — reset after response, no per-object free.

4. jemalloc tuning

bash

# Use jemalloc as system allocator
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.2 ./myapp

# Runtime tuning
export MALLOC_CONF="background_thread:true,dirty_decay_ms:1000,muzzy_decay_ms:1000"

# Profiling build
# ./configure --enable-prof
export MALLOC_CONF="prof:true,prof_active:true,lg_prof_sample:19"

jemalloc concepts:

Size classes — rounded allocation sizes
tcache — per-thread cache for hot sizes
arenas — reduce contention across threads

bash

# Statistics
export MALLOC_CONF="stats_print:true"
# prints on exit, or:
mallctl("epoch", ...); mallctl("stats.allocated", ...);

5. mimalloc

bash

# Use mimalloc
LD_PRELOAD=/usr/lib/libmimalloc.so ./myapp

# Environment options
export MIMALLOC_SHOW_STATS=1
export MIMALLOC_PAGE_RESET=1

mimalloc hierarchy: segment → page → block. Generally lower metadata overhead than jemalloc.

bash

# Statistics at exit
MIMALLOC_SHOW_STATS=1 ./myapp

6. tcmalloc thread-caching

bash

LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libtcmalloc.so.4 ./myapp

# Environment
export TCMALLOC_SAMPLE_PARAMETER=524288  # sampling profiler

Per-thread caches for small objects; central heap for larger allocations.

7. Rust GlobalAlloc

rust

use std::alloc::{GlobalAlloc, Layout, System};
use std::sync::atomic::{AtomicUsize, Ordering};

struct TrackingAllocator;

static ALLOCATED: AtomicUsize = AtomicUsize::new(0);

unsafe impl GlobalAlloc for TrackingAllocator {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        let ptr = System.alloc(layout);
        if !ptr.is_null() {
            ALLOCATED.fetch_add(layout.size(), Ordering::Relaxed);
        }
        ptr
    }
    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        System.dealloc(ptr, layout);
        ALLOCATED.fetch_sub(layout.size(), Ordering::Relaxed);
    }
}

#[global_allocator]
static GLOBAL: TrackingAllocator = TrackingAllocator;

For #![no_std] with alloc crate, implement GlobalAlloc without System.

8. Fragmentation metrics

Type	Definition	Detection
Internal	Allocated block larger than requested	Allocator stats; size class rounding
External	Free memory not usable for request	`mallinfo`/`malloc_info`; RSS vs heap

bash

# glibc malloc_info
malloc_info(0, stdout);

# jemalloc
jeprof --show_bytes ./myapp jeprof.heap

9. Benchmarking

bash

# mimalloc bench (if built from source)
cd mimalloc && mkdir build && cd build
cmake .. && make
./mimalloc-bench

# Custom microbenchmark pattern
perf stat -e cycles,instructions ./allocator_bench --threads 8 --size 64

Compare: single-thread alloc/free, multi-thread contention, mixed size distribution.

Common Problems

Symptom	Cause	Fix
Pool alloc returns NULL	Free list exhausted	Increase pool size; leak check
jemalloc RSS won't drop	Dirty page decay slow	Lower `dirty_decay_ms`; `madvise`
Arena OOM	No reset between phases	`arena_reset` or chain arenas
Rust allocator UB	Wrong Layout in dealloc	Store size/align with allocation
Worse perf with mimalloc	Wrong workload fit	Benchmark; try jemalloc
High external fragmentation	Long-lived mixed sizes	Segregate by lifetime; pools

Related Skills

skills/allocators/numa-programming — NUMA-aware allocation
skills/rust/rust-no-std — custom allocators in embedded Rust
skills/profilers/heaptrack — allocation hotspot profiling
skills/profilers/valgrind — heap leak detection
skills/low-level-programming/cpu-cache-opt — allocator alignment and false sharing
skills/kernel/kernel-internals — SLUB/buddy kernel allocators

사용 방법

시작 전 확인

Custom Allocators

Purpose

When to Use

Workflow

1. Allocator taxonomy

2. Simple pool allocator in C

3. Arena allocator

4. jemalloc tuning

5. mimalloc

6. tcmalloc thread-caching

7. Rust GlobalAlloc

8. Fragmentation metrics

9. Benchmarking

Common Problems

Related Skills

더 많은 Skills

core-dumps

ebpf

flamegraphs

gdb