hakmem/core/hakmem_tiny_ultra_simple.inc

// hakmem_tiny_ultra_simple.inc
// Phase 6-1.5: Ultra-Simple Fast Path integrated with existing HAKMEM
//
// Design: "Simple Front + Smart Back" (inspired by Mid-Large HAKX +171%)
// - Front: Ultra-simple TLS SLL (reuse existing g_tls_sll_head[])
// - Back: Existing SuperSlab + ACE + Learning layer
//
// Key insight: HAKMEM already HAS the infrastructure!
// - g_tls_sll_head[] exists (line 492 of hakmem_tiny.c)
// - sll_refill_small_from_ss() exists (hakmem_tiny_refill.inc.h:187)
// - Just need to remove the overhead layers!

#ifndef HAKMEM_TINY_ULTRA_SIMPLE_INC
#define HAKMEM_TINY_ULTRA_SIMPLE_INC

// ============================================================================
// Phase 6-1.5: Ultra-Simple Allocator (uses existing infrastructure)
// ============================================================================
// This replaces the complex multi-layer fast path with a 3-4 instruction path
// while keeping all existing backend infrastructure (SuperSlab, ACE, Learning)

// Forward declarations for external TLS variables and functions
extern __thread void* g_tls_sll_head[TINY_NUM_CLASSES];
extern __thread uint32_t g_tls_sll_count[TINY_NUM_CLASSES];

static __thread int g_ultra_simple_called = 0;

// NOTE: These functions are NOT static because they need to be called from hakmem.c
// They MUST be defined in hakmem_tiny.c where TLS variables are accessible
void* hak_tiny_alloc_ultra_simple(size_t size) {
    // DEBUG: Mark that we're using ultra_simple path (disabled in release)
#ifdef HAKMEM_DEBUG_VERBOSE
    if (!g_ultra_simple_called) {
        fprintf(stderr, "[PHASE 6-1.5] Ultra-simple path ACTIVE!\n");
        g_ultra_simple_called = 1;
    }
#endif

    // 1. Size → class (inline function, existing)
    int class_idx = hak_tiny_size_to_class(size);
    if (__builtin_expect(class_idx < 0, 0)) {
        return NULL;  // >1KB
    }

    // 2. Ultra-fast path: Pop from existing TLS SLL (Phase 6-1 style!)
    //    This is IDENTICAL to Phase 6-1 but uses existing g_tls_sll_head[]
    void* head = g_tls_sll_head[class_idx];
    if (__builtin_expect(head != NULL, 1)) {
        g_tls_sll_head[class_idx] = *(void**)head;  // 1-instruction pop!
        if (g_tls_sll_count[class_idx] > 0) g_tls_sll_count[class_idx]--;
        HAK_RET_ALLOC(class_idx, head);
    }

    // 3. Miss: Refill from existing SuperSlab infrastructure
    //    This gives us ACE, Learning layer, L25 integration for free!
    // Tunable refill count (env: HAKMEM_TINY_REFILL_COUNT, default 32)
    static int s_refill_count = 0;
    if (__builtin_expect(s_refill_count == 0, 0)) {
        int def = 32;  // smaller refill improves warm-up and reuse density
        char* env = getenv("HAKMEM_TINY_REFILL_COUNT");
        int v = (env ? atoi(env) : def);
        if (v < 8) v = 8;            // clamp to sane range
        if (v > 256) v = 256;
        s_refill_count = v;
    }
    int refill_count = s_refill_count;
    if (sll_refill_small_from_ss(class_idx, refill_count) > 0) {
        head = g_tls_sll_head[class_idx];
        if (head) {
            g_tls_sll_head[class_idx] = *(void**)head;
            if (g_tls_sll_count[class_idx] > 0) g_tls_sll_count[class_idx]--;
            HAK_RET_ALLOC(class_idx, head);
        }
    }

    // 4. Fallback to slow path (existing infrastructure)
    void* slow_ptr = hak_tiny_alloc_slow(size, class_idx);
    if (slow_ptr) {
        HAK_RET_ALLOC(class_idx, slow_ptr);
    }
    return slow_ptr;
}

// ============================================================================
// Ultra-Simple Free Path (bypasses free.part.0 complexity)
// ============================================================================
// This eliminates the 38.43% free path overhead identified by perf analysis:
// - free.part.0: 15.83%
// - mid_lookup: 9.55%
// - pthread locks: 8.81%
// Just 2-3 instructions: owner check → push to TLS SLL

static __thread int g_ultra_simple_free_called = 0;
static __thread uint64_t g_ultra_simple_free_count = 0;

// Ultra-fast class guess from pointer alignment (Phase 6-1.6: CTZ optimization)
// This is FAST but may be wrong - validation happens later!
static inline int guess_class_from_alignment(void* ptr) {
    uintptr_t addr = (uintptr_t)ptr;

    // Quick check: not 8-byte aligned → not Tiny
    if (__builtin_expect((addr & 7) != 0, 0)) return -1;

    // Fast path: Use Count Trailing Zeros (1 instruction!)
    // Tiny classes: 8B(cls0), 16B(cls1), 32B(cls2), 64B(cls3), 128B(cls4), 256B(cls5), 512B(cls6), 1KB(cls7)
    // 8B:   addr ends ...000    → ctz=3  → cls=0
    // 16B:  addr ends ...0000   → ctz=4  → cls=1
    // 32B:  addr ends ...00000  → ctz=5  → cls=2
    // 64B:  addr ends ...000000 → ctz=6  → cls=3
    int trailing_zeros = __builtin_ctzl(addr);
    int class_idx = trailing_zeros - 3;  // Subtract 3 (log2(8))

    // Clamp to valid range (0-7 for Tiny classes)
    if (__builtin_expect(class_idx < 0 || class_idx >= TINY_NUM_CLASSES, 0)) {
        return -1;  // Invalid alignment
    }

    return class_idx;
}

// NOTE: This function is NOT static because it needs to be called from hakmem.c
// It MUST be defined in hakmem_tiny.c where TLS variables are accessible
void hak_tiny_free_ultra_simple(void* ptr) {
    // DEBUG: Mark that we're using ultra_simple free path (disabled in release)
#ifdef HAKMEM_DEBUG_VERBOSE
    if (!g_ultra_simple_free_called) {
        fprintf(stderr, "[PHASE 6-1.5] Ultra-simple FREE path ACTIVE (LAZY VALIDATION)!\n");
        g_ultra_simple_free_called = 1;
    }
#endif

    // Prefer safe same-thread detection over pure alignment guessing to avoid
    // capturing cross-thread frees into the wrong TLS SLL (Larson MT case).

    // 1) SuperSlab-backed tiny pointer?
    if (__builtin_expect(g_use_superslab != 0, 1)) {
        SuperSlab* ss = hak_super_lookup(ptr);
        if (__builtin_expect(ss != NULL && ss->magic == SUPERSLAB_MAGIC, 0)) {
            int slab_idx = slab_index_for(ss, ptr);
            TinySlabMeta* meta = &ss->slabs[slab_idx];
            uint32_t self_tid = tiny_self_u32();
            if (__builtin_expect(meta->owner_tid == self_tid, 1)) {
                int class_idx = ss->size_class;
                *(void**)ptr = g_tls_sll_head[class_idx];
                g_tls_sll_head[class_idx] = ptr;
                g_tls_sll_count[class_idx]++;
                // Active accounting on free
                ss_active_dec_one(ss);
                return;
            }
            // Cross-thread free → delegate to full tiny free
            hak_tiny_free(ptr);
            return;
        }
    }

    // 2) Legacy TinySlab-backed pointer?
    TinySlab* slab = hak_tiny_owner_slab(ptr);
    if (__builtin_expect(slab != NULL, 0)) {
        if (__builtin_expect(pthread_equal(slab->owner_tid, tiny_self_pt()), 1)) {
            int class_idx = slab->class_idx;
            *(void**)ptr = g_tls_sll_head[class_idx];
            g_tls_sll_head[class_idx] = ptr;
            g_tls_sll_count[class_idx]++;
            return;
        }
        // Cross-thread free → precise path with known slab
        hak_tiny_free_with_slab(ptr, slab);
        return;
    }

    // 3) Fallback: Not a tiny allocation (or unknown) → delegate
    hak_free_at(ptr, 0, 0);
}

#endif // HAKMEM_TINY_ULTRA_SIMPLE_INC