hakmem/core/hakmem_tiny_refill.inc.h

// hakmem_tiny_refill.inc.h
// Phase 2D-1: Hot-path inline functions - Refill operations
//
// This file contains hot-path refill functions for various allocation tiers.
// These functions are extracted from hakmem_tiny.c to improve maintainability and
// reduce the main file size by approximately 280 lines.
//
// Functions handle:
// - tiny_fast_refill_and_take: Fast cache refill (lines 584-622, 39 lines)
// - quick_refill_from_sll: Quick slot refill from SLL (lines 918-936, 19 lines)
// - quick_refill_from_mag: Quick slot refill from magazine (lines 938-949, 12 lines)
// - sll_refill_small_from_ss: SLL refill from superslab (lines 952-996, 45 lines)
// - superslab_tls_bump_fast: TLS bump allocation (lines 1016-1060, 45 lines)
// - frontend_refill_fc: Frontend fast cache refill (lines 1063-1106, 44 lines)
// - bulk_mag_to_sll_if_room: Magazine to SLL bulk transfer (lines 1133-1154, 22 lines)
// - ultra_refill_sll: Ultra-mode SLL refill (lines 1178-1233, 56 lines)

#ifndef HAKMEM_TINY_REFILL_INC_H
#define HAKMEM_TINY_REFILL_INC_H

#include "hakmem_tiny.h"
#include "hakmem_tiny_superslab.h"
#include "hakmem_tiny_magazine.h"
#include "hakmem_tiny_tls_list.h"
#include "tiny_box_geometry.h"  // Box 3: Geometry & Capacity Calculator
#include "hakmem_super_registry.h"  // For hak_super_lookup (Debug validation)
#include "superslab/superslab_inline.h"  // For slab_index_for/ss_slabs_capacity (Debug validation)
#include "box/tls_sll_box.h"    // Box TLS-SLL: Safe SLL operations API
#include <stdint.h>
#include <pthread.h>
#include <stdlib.h>

// External declarations for TLS variables and globals
extern int g_fast_enable;
extern uint16_t g_fast_cap[TINY_NUM_CLASSES];
extern __thread void* g_fast_head[TINY_NUM_CLASSES];
extern __thread uint16_t g_fast_count[TINY_NUM_CLASSES];

extern int g_tls_list_enable;
extern int g_tls_sll_enable;
extern __thread void* g_tls_sll_head[TINY_NUM_CLASSES];
extern __thread uint32_t g_tls_sll_count[TINY_NUM_CLASSES];

extern int g_use_superslab;
extern int g_ultra_bump_shadow;
extern int g_bump_chunk;
extern __thread uint8_t* g_tls_bcur[TINY_NUM_CLASSES];
extern __thread uint8_t* g_tls_bend[TINY_NUM_CLASSES];

extern int g_fastcache_enable;
extern int g_quick_enable;

// External variable declarations
// Note: TinyTLSSlab, TinyFastCache, and TinyQuickSlot types must be defined before including this file
extern __thread TinyTLSSlab g_tls_slabs[TINY_NUM_CLASSES];
extern TinyPool g_tiny_pool;
extern PaddedLock g_tiny_class_locks[TINY_NUM_CLASSES];
extern __thread TinyFastCache g_fast_cache[TINY_NUM_CLASSES];
extern __thread TinyQuickSlot g_tls_quick[TINY_NUM_CLASSES];

// Frontend fill target
extern _Atomic uint32_t g_frontend_fill_target[TINY_NUM_CLASSES];

// Debug counters
#if HAKMEM_DEBUG_COUNTERS
extern uint64_t g_bump_hits[TINY_NUM_CLASSES];
extern uint64_t g_bump_arms[TINY_NUM_CLASSES];
extern uint64_t g_path_refill_calls[TINY_NUM_CLASSES];
extern uint64_t g_ultra_refill_calls[TINY_NUM_CLASSES];
#define HAK_PATHDBG_INC(arr, idx) do { if (g_path_debug_enabled) { (arr)[(idx)]++; } } while(0)
#define HAK_ULTRADBG_INC(arr, idx) do { (arr)[(idx)]++; } while(0)
extern int g_path_debug_enabled;
#else
#define HAK_PATHDBG_INC(arr, idx) do { (void)(idx); } while(0)
#define HAK_ULTRADBG_INC(arr, idx) do { (void)(idx); } while(0)
#endif

// Tracepoint macros
#ifndef HAK_TP1
#define HAK_TP1(name, idx) do { (void)(idx); } while(0)
#endif

// Forward declarations for functions used in this file
static inline void* tiny_fast_pop(int class_idx);
static inline int tiny_fast_push(int class_idx, void* ptr);
static inline int tls_refill_from_tls_slab(int class_idx, TinyTLSList* tls, uint32_t want);
static inline uint32_t sll_cap_for_class(int class_idx, uint32_t mag_cap);
static SuperSlab* superslab_refill(int class_idx);
static void* slab_data_start(SuperSlab* ss, int slab_idx);
static inline uint8_t* tiny_slab_base_for(SuperSlab* ss, int slab_idx);
static inline void ss_active_add(SuperSlab* ss, uint32_t n);
static inline void ss_active_inc(SuperSlab* ss);
static TinySlab* allocate_new_slab(int class_idx);
static void move_to_full_list(int class_idx, struct TinySlab* target_slab);
static int hak_tiny_find_free_block(TinySlab* slab);
static void hak_tiny_set_used(TinySlab* slab, int block_idx);
static inline int ultra_batch_for_class(int class_idx);
static inline int ultra_sll_cap_for_class(int class_idx);
// Note: tiny_small_mags_init_once and tiny_mag_init_if_needed are declared in hakmem_tiny_magazine.h
static void eventq_push(int class_idx, uint32_t size);

// Debug-only: Validate that a base node belongs to the expected Tiny SuperSlab and is stride-aligned
#if !HAKMEM_BUILD_RELEASE
static inline void tiny_debug_validate_node_base(int class_idx, void* node, const char* where) {
    if ((uintptr_t)node < 4096) {
        fprintf(stderr, "[SLL_NODE_SMALL] %s: node=%p cls=%d\n", where, node, class_idx);
        abort();
    }
    SuperSlab* ss = hak_super_lookup(node);
    if (!ss) {
        fprintf(stderr, "[SLL_NODE_UNKNOWN] %s: node=%p cls=%d\n", where, node, class_idx);
        abort();
    }
    int ocls = ss->size_class;
    if (ocls == 7 || ocls != class_idx) {
        fprintf(stderr, "[SLL_NODE_CLASS_MISMATCH] %s: node=%p cls=%d owner_cls=%d\n", where, node, class_idx, ocls);
        abort();
    }
    int slab_idx = slab_index_for(ss, node);
    if (slab_idx < 0 || slab_idx >= ss_slabs_capacity(ss)) {
        fprintf(stderr, "[SLL_NODE_SLAB_OOB] %s: node=%p slab_idx=%d cap=%d\n", where, node, slab_idx, ss_slabs_capacity(ss));
        abort();
    }
    uint8_t* base = tiny_slab_base_for_geometry(ss, slab_idx);
    size_t usable = tiny_usable_bytes_for_slab(slab_idx);
    size_t stride = tiny_stride_for_class(ocls);
    uintptr_t a = (uintptr_t)node;
    if (a < (uintptr_t)base || a >= (uintptr_t)base + usable) {
        fprintf(stderr, "[SLL_NODE_RANGE] %s: node=%p base=%p usable=%zu\n", where, node, base, usable);
        abort();
    }
    size_t off = (size_t)(a - (uintptr_t)base);
    if (off % stride != 0) {
        fprintf(stderr, "[SLL_NODE_MISALIGNED] %s: node=%p off=%zu stride=%zu base=%p\n", where, node, off, stride, base);
        abort();
    }
}
#else
static inline void tiny_debug_validate_node_base(int class_idx, void* node, const char* where) { (void)class_idx; (void)node; (void)where; }
#endif

// Fast cache refill and take operation
static inline void* tiny_fast_refill_and_take(int class_idx, TinyTLSList* tls) {
    void* direct = tiny_fast_pop(class_idx);
    if (direct) return direct;
    uint16_t cap = g_fast_cap[class_idx];
    if (cap == 0) return NULL;
    uint16_t count = g_fast_count[class_idx];
    uint16_t need = cap > count ? (uint16_t)(cap - count) : 0;
    if (need == 0) return NULL;
    uint32_t have = tls->count;
    if (have < need) {
        uint32_t want = need - have;
        uint32_t thresh = tls_list_refill_threshold(tls);
        if (want < thresh) want = thresh;
        tls_refill_from_tls_slab(class_idx, tls, want);
    }
    void* batch_head = NULL;
    void* batch_tail = NULL;
    uint32_t taken = tls_list_bulk_take(tls, need, &batch_head, &batch_tail, class_idx);
    if (taken == 0u || batch_head == NULL) {
        return NULL;
    }

    void* ret = batch_head;
#if HAKMEM_TINY_HEADER_CLASSIDX
    const size_t next_off_tls = (class_idx == 7) ? 0 : 1;
#else
    const size_t next_off_tls = 0;
#endif
    void* node = *(void**)((uint8_t*)ret + next_off_tls);
    uint32_t remaining = (taken > 0u) ? (taken - 1u) : 0u;

    while (node && remaining > 0u) {
        void* next = *(void**)((uint8_t*)node + next_off_tls);
        if (tiny_fast_push(class_idx, node)) {
            node = next;
            remaining--;
        } else {
            // Push failed, return remaining to TLS
            tls_list_bulk_put(tls, node, batch_tail, remaining, class_idx);
            return ret;
        }
    }
    return ret;
}

// Quick slot refill from SLL
static inline int quick_refill_from_sll(int class_idx) {
    if (!g_tls_sll_enable) return 0;
    TinyQuickSlot* qs = &g_tls_quick[class_idx];
    int room = (int)(QUICK_CAP - qs->top);
    if (room <= 0) return 0;
    // Limit burst to a tiny constant to reduce loop/branches
    if (room > 2) room = 2;
    int filled = 0;
    while (room > 0) {
        // CRITICAL: Use Box TLS-SLL API to avoid race condition (rbp=0xa0 SEGV)
        void* head = NULL;
        if (!tls_sll_pop(class_idx, &head)) break;
        // One-shot validation for the first pop
#if !HAKMEM_BUILD_RELEASE
        do { static _Atomic int once = 0; int exp = 0; if (atomic_compare_exchange_strong(&once, &exp, 1)) { tiny_debug_validate_node_base(class_idx, head, "quick_refill_from_sll"); } } while (0);
#endif
        qs->items[qs->top++] = head;
        room--; filled++;
    }
    if (filled > 0) HAK_TP1(quick_refill_sll, class_idx);
    if (filled > 0) {
        extern unsigned long long g_front_quick_hit[];
        g_front_quick_hit[class_idx]++;
    }
    return filled;
}

// Quick slot refill from magazine
static inline int quick_refill_from_mag(int class_idx) {
    TinyTLSMag* mag = &g_tls_mags[class_idx];
    if (mag->top <= 0) return 0;
    TinyQuickSlot* qs = &g_tls_quick[class_idx];
    int room = (int)(QUICK_CAP - qs->top);
    if (room <= 0) return 0;
    // Only a single transfer from magazine to minimize overhead
    int take = (mag->top > 0 && room > 0) ? 1 : 0;
    for (int i = 0; i < take; i++) { qs->items[qs->top++] = mag->items[--mag->top].ptr; }
    if (take > 0) HAK_TP1(quick_refill_mag, class_idx);
    return take;
}

// P0 optimization: Batch refill（A/Bテスト用ランタイムゲートで呼び分け）
// - デフォルトはOFF（環境変数 HAKMEM_TINY_P0_ENABLE=1 で有効化）
#include "hakmem_tiny_refill_p0.inc.h"

// Box 3 wrapper: verify linear carve stays within slab usable bytes (Fail-Fast)
// DEPRECATED: Use tiny_carve_guard_verbose() from Box 3 directly
static inline int tiny_linear_carve_guard(TinyTLSSlab* tls,
                                          TinySlabMeta* meta,
                                          size_t stride,
                                          uint32_t reserve,
                                          const char* stage) {
    if (!tls || !meta) return 0;
    int class_idx = tls->ss ? tls->ss->size_class : -1;
    return tiny_carve_guard_verbose(stage,
                                    class_idx,
                                    tls->slab_idx,
                                    meta->carved,
                                    meta->used,
                                    meta->capacity,
                                    stride,
                                    reserve);
}

// Refill a few nodes directly into TLS SLL from TLS-cached SuperSlab (owner-thread only)
// Note: If HAKMEM_TINY_P0_BATCH_REFILL is enabled, sll_refill_batch_from_ss is used instead
#if !HAKMEM_TINY_P0_BATCH_REFILL
// Phase 6-1.7: Export for box refactor (Box 5 needs access from hakmem.c)
// Note: Force non-inline to provide linkable definition for LTO
#ifdef HAKMEM_TINY_PHASE6_BOX_REFACTOR
__attribute__((noinline)) int sll_refill_small_from_ss(int class_idx, int max_take) {
#else
static inline int sll_refill_small_from_ss(int class_idx, int max_take) {
#endif
    // CRITICAL: C7 (1KB) is headerless - incompatible with TLS SLL refill
    if (__builtin_expect(class_idx == 7, 0)) {
        return 0;  // C7 uses slow path exclusively
    }

    if (!g_use_superslab || max_take <= 0) return 0;
    // ランタイムA/B: P0を有効化している場合はバッチrefillへ委譲
    do {
        // 既定: OFF（HAKMEM_TINY_P0_ENABLE=1 で有効化）
        static int g_p0_enable = -1;
        if (__builtin_expect(g_p0_enable == -1, 0)) {
            const char* e = getenv("HAKMEM_TINY_P0_ENABLE");
            // 環境変数が'1'のときだけ有効、それ以外（未設定含む）は無効
            g_p0_enable = (e && *e && *e == '1') ? 1 : 0;
        }
        if (__builtin_expect(g_p0_enable, 0)) {
            return sll_refill_batch_from_ss(class_idx, max_take);
        }
    } while (0);
    TinyTLSSlab* tls = &g_tls_slabs[class_idx];
    if (!tls->ss) {
        // Try to obtain a SuperSlab for this class
        if (superslab_refill(class_idx) == NULL) return 0;
        // CRITICAL FIX: Reload tls pointer after superslab_refill() binds new slab
        tls = &g_tls_slabs[class_idx];
    }
    TinySlabMeta* meta = tls->meta;
    if (!meta) return 0;

    // Class 4/5/6/7 special-case: simple batch refill (favor linear carve, minimal branching)
    // Optional gate for class3 via env: HAKMEM_TINY_SIMPLE_REFILL_C3=1
    static int g_simple_c3 = -1;
    if (__builtin_expect(g_simple_c3 == -1, 0)) {
        const char* e = getenv("HAKMEM_TINY_SIMPLE_REFILL_C3");
        g_simple_c3 = (e && *e && *e != '0') ? 1 : 0;
    }
    if (__builtin_expect(class_idx >= 4 || (class_idx == 3 && g_simple_c3), 0)) {
        uint32_t sll_cap = sll_cap_for_class(class_idx, (uint32_t)TINY_TLS_MAG_CAP);
        int room = (int)sll_cap - (int)g_tls_sll_count[class_idx];
        if (room <= 0) return 0;
        int take = max_take < room ? max_take : room;
        int taken = 0;
        // Box 3: Get stride (block size + header, except C7 which is headerless)
        size_t bs = tiny_stride_for_class(class_idx);
        for (; taken < take;) {
            // Linear first (LIKELY for class7)
            if (__builtin_expect(meta->freelist == NULL && meta->carved < meta->capacity, 1)) {
                if (__builtin_expect(!tiny_linear_carve_guard(tls, meta, bs, 1, "simple"), 0)) {
                    abort();
                }
                // Box 3: Get slab base (handles Slab 0 offset)
                uint8_t* base = tiny_slab_base_for_geometry(tls->ss, tls->slab_idx);
                void* p = tiny_block_at_index(base, meta->carved, bs);
                meta->carved++;
                meta->used++;
                // CRITICAL: Use Box TLS-SLL API (C7-safe, no race)
                if (!tls_sll_push(class_idx, p, sll_cap)) {
                    // SLL full (should not happen, room was checked)
                    meta->used--; meta->carved--;  // Rollback
                    break;
                }
                ss_active_inc(tls->ss);
                taken++;
                continue;
            }
            // Freelist fallback
            if (__builtin_expect(meta->freelist != NULL, 0)) {
                void* p = meta->freelist;
                meta->freelist = *(void**)p;
                meta->used++;
                // CRITICAL: Use Box TLS-SLL API (C7-safe, no race)
                if (!tls_sll_push(class_idx, p, sll_cap)) {
                    // SLL full (should not happen, room was checked)
                    *(void**)p = meta->freelist;  // Rollback freelist
                    meta->freelist = p;
                    meta->used--;
                    break;
                }
                ss_active_inc(tls->ss);
                taken++;
                continue;
            }
            // Need another slab with space
            if (__builtin_expect(superslab_refill(class_idx) == NULL, 0)) break;
            // CRITICAL FIX: Reload tls pointer after superslab_refill() binds new slab
            tls = &g_tls_slabs[class_idx];
            meta = tls->meta; // refresh after refill
        }
        return taken;
    }

    // Compute how many we can actually push into SLL without overflow
    uint32_t sll_cap = sll_cap_for_class(class_idx, (uint32_t)TINY_TLS_MAG_CAP);
    int room = (int)sll_cap - (int)g_tls_sll_count[class_idx];
    if (room <= 0) return 0;
    int take = max_take < room ? max_take : room;

    int taken = 0;
    // Box 3: Get stride (block size + header, except C7 which is headerless)
    size_t bs = tiny_stride_for_class(class_idx);
    while (taken < take) {
        void* p = NULL;
        if (__builtin_expect(meta->freelist != NULL, 0)) {
            p = meta->freelist; meta->freelist = *(void**)p; meta->used++;
            // Track active blocks reserved into TLS SLL
            ss_active_inc(tls->ss);
        } else if (__builtin_expect(meta->carved < meta->capacity, 1)) {
            if (__builtin_expect(!tiny_linear_carve_guard(tls, meta, bs, 1, "general"), 0)) {
                abort();
            }
            // Box 3: Get slab base and calculate block address
            uint8_t* slab_start = tiny_slab_base_for_geometry(tls->ss, tls->slab_idx);
            p = tiny_block_at_index(slab_start, meta->carved, bs);
            meta->carved++;
            meta->used++;
            // Track active blocks reserved into TLS SLL
            ss_active_inc(tls->ss);
        } else {
            // Move to another slab with space
            if (superslab_refill(class_idx) == NULL) break;
            // CRITICAL FIX: Reload tls pointer after superslab_refill() binds new slab
            tls = &g_tls_slabs[class_idx];
            meta = tls->meta; // refresh after refill
            continue;
        }
        if (!p) break;
        // CRITICAL: Use Box TLS-SLL API (C7-safe, no race)
        if (!tls_sll_push(class_idx, p, sll_cap)) {
            // SLL full (should not happen, room was checked)
            // Rollback: need to return block to meta (complex, just break)
            break;
        }
        taken++;
    }
    return taken;
}
#endif // !HAKMEM_TINY_P0_BATCH_REFILL

// Ultra-Bump TLS shadow try: returns pointer when a TLS bump window is armed
// or can be armed by reserving a small chunk from the current SuperSlab meta.
static inline void* superslab_tls_bump_fast(int class_idx) {
    if (!g_ultra_bump_shadow || !g_use_superslab) return NULL;
    // Serve from armed TLS window if present
    uint8_t* cur = g_tls_bcur[class_idx];
    if (__builtin_expect(cur != NULL, 0)) {
        uint8_t* end = g_tls_bend[class_idx];
        size_t bs = g_tiny_class_sizes[class_idx];
        if (__builtin_expect(cur <= end - bs, 1)) {
            g_tls_bcur[class_idx] = cur + bs;
#if HAKMEM_DEBUG_COUNTERS
            g_bump_hits[class_idx]++;
#endif
            HAK_TP1(bump_hit, class_idx);
            return (void*)cur;
        }
        // Window exhausted
        g_tls_bcur[class_idx] = NULL;
        g_tls_bend[class_idx] = NULL;
    }
    // Arm a new window from TLS-cached SuperSlab meta (linear mode only)
    TinyTLSSlab* tls = &g_tls_slabs[class_idx];
    TinySlabMeta* meta = tls->meta;
    if (!meta || meta->freelist != NULL) return NULL;  // linear mode only
    // Use monotonic 'carved' for window arming
    uint16_t carved = meta->carved;
    uint16_t cap  = meta->capacity;
    if (carved >= cap) return NULL;
    uint32_t avail = (uint32_t)cap - (uint32_t)carved;
    uint32_t chunk = (g_bump_chunk > 0 ? (uint32_t)g_bump_chunk : 1u);
    if (chunk > avail) chunk = avail;
    // Box 3: Get stride and slab base
    size_t bs = tiny_stride_for_class(tls->ss->size_class);
    uint8_t* base = tls->slab_base ? tls->slab_base : tiny_slab_base_for_geometry(tls->ss, tls->slab_idx);
    if (__builtin_expect(!tiny_linear_carve_guard(tls, meta, bs, chunk, "tls_bump"), 0)) {
        abort();
    }
    uint8_t* start = base + ((size_t)carved * bs);
    // Reserve the chunk: advance carved and used accordingly
    meta->carved = (uint16_t)(carved + (uint16_t)chunk);
    meta->used   = (uint16_t)(meta->used + (uint16_t)chunk);
    // Account all reserved blocks as active in SuperSlab
    ss_active_add(tls->ss, chunk);
#if HAKMEM_DEBUG_COUNTERS
    g_bump_arms[class_idx]++;
#endif
    g_tls_bcur[class_idx] = start + bs;
    g_tls_bend[class_idx] = start + (size_t)chunk * bs;
    return (void*)start;
}

// Frontend: refill FastCache directly from TLS active slab (owner-only) or adopt a slab
static inline int frontend_refill_fc(int class_idx) {
    TinyFastCache* fc = &g_fast_cache[class_idx];
    int room = TINY_FASTCACHE_CAP - fc->top;
    if (room <= 0) return 0;
    // Target refill (conservative for safety)
    int need = ultra_batch_for_class(class_idx);
    int tgt = atomic_load_explicit(&g_frontend_fill_target[class_idx], memory_order_relaxed);
    if (tgt > 0 && tgt < need) need = tgt;
    if (need > room) need = room;
    if (need <= 0) return 0;

    int filled = 0;

    // Step A: First bulk transfer from TLS SLL to FastCache (lock-free, O(1))
    // CRITICAL: Use Box TLS-SLL API to avoid race condition (rbp=0xa0 SEGV)
    if (g_tls_sll_enable) {
        while (need > 0) {
            void* h = NULL;
            if (!tls_sll_pop(class_idx, &h)) break;
            // One-shot validation for the first pop into FastCache
#if !HAKMEM_BUILD_RELEASE
            do { static _Atomic int once_fc = 0; int exp2 = 0; if (atomic_compare_exchange_strong(&once_fc, &exp2, 1)) { tiny_debug_validate_node_base(class_idx, h, "frontend_refill_fc"); } } while (0);
#endif
            fc->items[fc->top++] = h;
            need--; filled++;
            if (fc->top >= TINY_FASTCACHE_CAP) break;
        }
    }

    // Step B: If still not enough, transfer from TLS Magazine (lock-free, O(1))
    if (need > 0) {
        tiny_small_mags_init_once();
        if (class_idx > 3) tiny_mag_init_if_needed(class_idx);
        TinyTLSMag* mag = &g_tls_mags[class_idx];
        while (need > 0 && mag->top > 0 && fc->top < TINY_FASTCACHE_CAP) {
            void* p = mag->items[--mag->top].ptr;
            fc->items[fc->top++] = p;
            need--; filled++;
        }
    }

    if (filled > 0) {
        eventq_push(class_idx, (uint32_t)g_tiny_class_sizes[class_idx]);
        HAK_PATHDBG_INC(g_path_refill_calls, class_idx);
        return 1;
    }
    return 0;
}

// Move up to 'n' items from TLS magazine to SLL if SLL has room (lock-free).
static inline int bulk_mag_to_sll_if_room(int class_idx, TinyTLSMag* mag, int n) {
    if (g_tls_list_enable) return 0;
    if (!g_tls_sll_enable || n <= 0) return 0;
    uint32_t cap = sll_cap_for_class(class_idx, (uint32_t)mag->cap);
    uint32_t have = g_tls_sll_count[class_idx];
    if (have >= cap) return 0;
    int room = (int)(cap - have);
    int avail = mag->top;
    // Hysteresis: avoid frequent tiny moves; take at least 8 if possible
    int take = (n < room ? n : room);
    if (take < 8 && avail >= 8 && room >= 8) take = 8;
    if (take > avail) take = avail;
    if (take <= 0) return 0;
    for (int i = 0; i < take; i++) {
        void* p = mag->items[--mag->top].ptr;
        if (!tls_sll_push(class_idx, p, cap)) {
            // No more room; return remaining items to magazine and stop
            mag->top++; // undo pop
            break;
        }
    }
    HAK_PATHDBG_INC(g_path_refill_calls, class_idx);
    return take;
}

// Ultra-mode (SLL-only) refill operation
static inline void ultra_refill_sll(int class_idx) {
    int need = ultra_batch_for_class(class_idx);
    HAK_ULTRADBG_INC(g_ultra_refill_calls, class_idx);
    int sll_cap = ultra_sll_cap_for_class(class_idx);
    pthread_mutex_t* lock = &g_tiny_class_locks[class_idx].m;
    pthread_mutex_lock(lock);
    TinySlab* slab = g_tiny_pool.free_slabs[class_idx];
    if (!slab) {
        slab = allocate_new_slab(class_idx);
        if (slab) {
            slab->next = g_tiny_pool.free_slabs[class_idx];
            g_tiny_pool.free_slabs[class_idx] = slab;
        }
    }
    if (slab) {
        // Box 3: Get stride (block size + header, except C7 which is headerless)
        size_t bs = tiny_stride_for_class(class_idx);
        int remaining = need;
        while (remaining > 0 && slab->free_count > 0) {
            if ((int)g_tls_sll_count[class_idx] >= sll_cap) break;
            int first = hak_tiny_find_free_block(slab);
            if (first < 0) break;
            // Allocate the first found block
            hak_tiny_set_used(slab, first);
            slab->free_count--;
            void* p0 = (char*)slab->base + ((size_t)first * bs);
            if (!tls_sll_push(class_idx, p0, (uint32_t)sll_cap)) {
                // SLL saturated; stop refilling
                break;
            }
            remaining--;
            // Try to allocate more from the same word to amortize scanning
            int word_idx = first / 64;
            uint64_t used = slab->bitmap[word_idx];
            uint64_t free_bits = ~used;
            while (remaining > 0 && free_bits && slab->free_count > 0) {
                if ((int)g_tls_sll_count[class_idx] >= sll_cap) break;
                int bit_idx = __builtin_ctzll(free_bits);
                int block_idx = word_idx * 64 + bit_idx;
                hak_tiny_set_used(slab, block_idx);
                slab->free_count--;
                void* p = (char*)slab->base + ((size_t)block_idx * bs);
                if (!tls_sll_push(class_idx, p, (uint32_t)sll_cap)) {
                    break;
                }
                remaining--;
                // Update free_bits for next iteration
                used = slab->bitmap[word_idx];
                free_bits = ~used;
            }
            if (slab->free_count == 0) {
                move_to_full_list(class_idx, slab);
                break;
            }
        }
    }
    pthread_mutex_unlock(lock);
}

#endif // HAKMEM_TINY_REFILL_INC_H