hakmem/core/box/pool_mid_desc.inc.h

// pool_mid_desc.inc.h — Box: Mid Page Descriptor Registry (64KiB pages)
#ifndef POOL_MID_DESC_INC_H
#define POOL_MID_DESC_INC_H

#define MID_DESC_BUCKETS 2048
typedef struct MidPageDesc {
    void* page;
    uint8_t class_idx;
    uint8_t _pad0;
    uint16_t _pad1;
    uint64_t owner_tid;
    atomic_int in_use;        // live allocations on this page
    int blocks_per_page;      // total blocks on this page
    atomic_int pending_dn;    // background DONTNEED enqueued
    struct MidPageDesc* next;
} MidPageDesc;
static pthread_mutex_t g_mid_desc_mu[MID_DESC_BUCKETS];
static MidPageDesc* g_mid_desc_head[MID_DESC_BUCKETS];

static inline uint32_t mid_desc_hash(void* page) {
    uintptr_t x = (uintptr_t)page >> 16; // 64KiB alignment granularity
    // mix
    x ^= x >> 33; x *= 0xff51afd7ed558ccdULL; x ^= x >> 33; x *= 0xc4ceb9fe1a85ec53ULL; x ^= x >> 33;
    return (uint32_t)(x & (MID_DESC_BUCKETS - 1));
}

// Thread-safe initialization using pthread_once
static pthread_once_t mid_desc_init_once_control = PTHREAD_ONCE_INIT;
static void mid_desc_init_impl(void) {
    for (int i = 0; i < MID_DESC_BUCKETS; i++) {
        pthread_mutex_init(&g_mid_desc_mu[i], NULL);
        g_mid_desc_head[i] = NULL;
    }
}
static void mid_desc_init_once(void) {
    pthread_once(&mid_desc_init_once_control, mid_desc_init_impl);
}

static void mid_desc_register(void* page, int class_idx, uint64_t owner_tid) {
    mid_desc_init_once();
    uint32_t h = mid_desc_hash(page);
    pthread_mutex_lock(&g_mid_desc_mu[h]);
    MidPageDesc* d = (MidPageDesc*)hkm_libc_malloc(sizeof(MidPageDesc));  // P0 Fix: Use libc malloc
    if (d) {
        d->page = page; d->class_idx = (uint8_t)class_idx; d->owner_tid = owner_tid; d->next = g_mid_desc_head[h];
        atomic_store(&d->in_use, 0);
        d->blocks_per_page = 0; // optional; not used for emptiness in P0
        atomic_store(&d->pending_dn, 0);
        g_mid_desc_head[h] = d;
    }
    pthread_mutex_unlock(&g_mid_desc_mu[h]);
}

static MidPageDesc* mid_desc_lookup(void* addr) {
    mid_desc_init_once();
    void* page = (void*)((uintptr_t)addr & ~((uintptr_t)POOL_PAGE_SIZE - 1));
    uint32_t h = mid_desc_hash(page);
    for (MidPageDesc* d = g_mid_desc_head[h]; d; d = d->next) {
        if (d->page == page) return d;
    }
    return NULL;
}

static void mid_desc_adopt(void* addr, int class_idx, uint64_t owner_tid) {
    if (owner_tid == 0) return;
    void* page = (void*)((uintptr_t)addr & ~((uintptr_t)POOL_PAGE_SIZE - 1));
    uint32_t h = mid_desc_hash(page);
    pthread_mutex_lock(&g_mid_desc_mu[h]);
    MidPageDesc* d = g_mid_desc_head[h];
    while (d) { if (d->page == page) break; d = d->next; }
    if (d) {
        if (d->owner_tid == 0) d->owner_tid = owner_tid;
    } else {
        MidPageDesc* nd = (MidPageDesc*)hkm_libc_malloc(sizeof(MidPageDesc));  // P0 Fix: Use libc malloc
        if (nd) { nd->page = page; nd->class_idx = (uint8_t)class_idx; nd->owner_tid = owner_tid; nd->next = g_mid_desc_head[h]; g_mid_desc_head[h] = nd; }
    }
    pthread_mutex_unlock(&g_mid_desc_mu[h]);
}

// Increment page in-use counter for given raw block pointer
static inline void mid_page_inuse_inc(void* raw) {
    MidPageDesc* d = mid_desc_lookup(raw);
    if (d) atomic_fetch_add_explicit(&d->in_use, 1, memory_order_relaxed);
}

// Decrement page in-use counter and enqueue DONTNEED when it drops to 0
extern int hak_batch_add_page(void* page, size_t size);
static inline void mid_page_inuse_dec_and_maybe_dn(void* raw) {
    MidPageDesc* d = mid_desc_lookup(raw);
    if (!d) return;
    int nv = atomic_fetch_sub_explicit(&d->in_use, 1, memory_order_relaxed) - 1;
    if (nv <= 0) {
        // Fire once per empty transition
        if (atomic_exchange_explicit(&d->pending_dn, 1, memory_order_acq_rel) == 0) {
            hak_batch_add_page(d->page, POOL_PAGE_SIZE);
        }
    }
}

#endif // POOL_MID_DESC_INC_H