hakmem/core/smallobject_cold_iface_v5.c

// smallobject_cold_iface_v5.c - SmallObject Cold Interface v5 (Phase v5-2)
//
// Purpose: Page refill/retire operations for SmallObject v5
// Design: C6-only implementation with segment-based allocation

#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include "box/smallobject_cold_iface_v5.h"
#include "box/smallsegment_v5_box.h"
#include "box/smallobject_hotbox_v5_box.h"
#include "box/smallobject_v5_env_box.h"
#include "tiny_region_id.h"  // For tiny_region_id_write_header

#ifndef likely
#define likely(x)   __builtin_expect(!!(x), 1)
#define unlikely(x) __builtin_expect(!!(x), 0)
#endif

// ============================================================================
// Cold Refill: Allocate a new page for the given class (Phase v5-2)
// ============================================================================

SmallPageMetaV5* small_cold_v5_refill_page(SmallHeapCtxV5* ctx, uint32_t class_idx) {
    (void)ctx;  // Not used in v5-2 C6-only implementation

    // Phase v5-2: C6-only implementation
    if (unlikely(class_idx != SMALL_HEAP_V5_C6_CLASS_IDX)) {
        return NULL;  // Only C6 supported in v5-2
    }

    // Step 1: Allocate a page from segment pool (reuses existing segments)
    SmallPageMetaV5* page = small_segment_v5_alloc_page();
    if (unlikely(!page)) {
        return NULL;  // OOM or TLS slot exhaustion
    }

    // Step 2: Get segment pointer (already set by alloc_page)
    SmallSegmentV5* seg = (SmallSegmentV5*)page->segment;
    if (unlikely(!seg)) {
        return NULL;
    }

    // Step 3: Initialize page metadata for C6
    page->class_idx = (uint8_t)class_idx;
    page->capacity = SMALL_SEGMENT_V5_PAGE_SIZE / SMALL_HEAP_V5_C6_BLOCK_SIZE;
    page->used = 0;
    page->flags = 0;

    // Step 4: Build freelist for the page
    // Page starts at: seg->base + (page_idx * SMALL_SEGMENT_V5_PAGE_SIZE)
    uintptr_t page_base = seg->base + ((uintptr_t)page->page_idx * SMALL_SEGMENT_V5_PAGE_SIZE);
    uint8_t* base = (uint8_t*)page_base;

    // Phase v5-4: Check header mode for carve-time optimization
    int header_mode = small_heap_v5_header_mode();

    // Build intrusive freelist (last to first for cache locality)
    void* freelist = NULL;
    for (int i = (int)page->capacity - 1; i >= 0; i--) {
        uint8_t* block = base + ((size_t)i * SMALL_HEAP_V5_C6_BLOCK_SIZE);

        // Phase v5-4: In light mode, write headers once during carve
        if (header_mode == SMALL_HEAP_V5_HEADER_MODE_LIGHT) {
            // Write header for this block (all blocks initialized at carve time)
            // This eliminates per-alloc header writes, improving performance by 2-4%
            tiny_region_id_write_header(block, class_idx);
        }

        void* next = freelist;
        memcpy(block, &next, sizeof(void*));
        freelist = block;
    }

    page->free_list = freelist;

    return page;
}

// ============================================================================
// Cold Retire: Return an empty page to the segment (Phase v5-2)
// ============================================================================

void small_cold_v5_retire_page(SmallHeapCtxV5* ctx, SmallPageMetaV5* page) {
    (void)ctx;  // Not used in v5-2

    if (unlikely(!page)) {
        return;
    }

    // Phase v5-2: C6-only implementation
    if (unlikely(page->class_idx != SMALL_HEAP_V5_C6_CLASS_IDX)) {
        return;  // Only C6 supported in v5-2
    }

    // Sanity check: Page should be empty (used == 0)
    if (page->used != 0) {
        return;  // Don't retire non-empty pages
    }

    // Reset page metadata to unused state
    page->free_list = NULL;
    page->used = 0;
    page->capacity = 0;
    page->class_idx = 0;
    page->flags = 0;

    // Free the page back to segment pool (makes it available for reuse)
    small_segment_v5_free_page(page);
}

// ============================================================================
// Remote Operations (Stub for Phase v5-2)
// ============================================================================

bool small_cold_v5_remote_push(SmallPageMetaV5* page, void* ptr, uint32_t tid) {
    (void)page;
    (void)ptr;
    (void)tid;
    return false;  // Not implemented in v5-2
}

void small_cold_v5_remote_drain(SmallHeapCtxV5* ctx) {
    (void)ctx;
    // Not implemented in v5-2
}