feat(heap): reorganize heap struct to satisfy cache alignements

Author: singaraiona

core/heap.h

@@ -35,6 +35,9 @@
 #define SLAB_CACHE_SIZE 64
 #define SLAB_ORDERS 5  // orders 5, 6, 7, 8, 9
 
+// Cache line size (typically 64 bytes on x86/ARM)
+#define CACHE_LINE_SIZE 64
+
 // Memory modes
 #define MMOD_INTERNAL 0xff
 #define MMOD_EXTERNAL_SIMPLE 0xfd
@@ -61,20 +64,29 @@ typedef struct block_t {
 } *block_p;
 
 // Small object slab cache for fast alloc/free of common sizes
+// count is FIRST - checked before stack access, avoids cache miss
 typedef struct slab_cache_t {
+    i64_t count;                     // current stack depth (check first!)
     block_p stack[SLAB_CACHE_SIZE];  // LIFO stack of freed blocks
-    i64_t count;                      // current stack depth
 } slab_cache_t;
 
 typedef struct heap_t {
-    i64_t id;
+    // ===== Cache line 1: hottest fields (allocation fast path) =====
+    i64_t avail;               // 8B - bitmask checked every alloc
+    i64_t id;                  // 8B - heap identity checked in free
+    block_p foreign_blocks;    // 8B - checked in worker free path
+    block_p backed_blocks;     // 8B - file-backed blocks
+    i64_t _pad_cacheline1[4];  // 32B - pad to 64B cache line
+
+    // ===== Slab caches (count field is first in each - fast path check) =====
+    slab_cache_t slabs[SLAB_ORDERS];  // small object caches for orders 5-9
+
+    // ===== Freelists (accessed for non-slab allocations) =====
     block_p freelist[MAX_POOL_ORDER + 2];  // free list of blocks by order
-    i64_t avail;                           // mask of available blocks by order
-    slab_cache_t slabs[SLAB_ORDERS];       // small object caches for orders 6-9
-    block_p foreign_blocks;                // foreign blocks (to be freed by the owner)
-    block_p backed_blocks;                 // backed blocks (to be unmapped)
-    memstat_t memstat;
-    c8_t swap_path[64];  // swap directory path
+
+    // ===== Cold fields (rarely accessed) =====
+    memstat_t memstat;   // statistics
+    c8_t swap_path[64];  // swap directory path (init only)
 } *heap_p;
 
 heap_p heap_create(i64_t id);

core/mmap.c

@@ -99,8 +99,19 @@ raw_p mmap_stack(i64_t size) {
 
 raw_p mmap_alloc(i64_t size) {
     raw_p ptr;
+    int flags = MAP_ANONYMOUS | MAP_SHARED | MAP_NONBLOCK | MAP_POPULATE;
+
+    // Try huge pages for large allocations (>= 2MB) - reduces TLB misses
+#ifdef MAP_HUGETLB
+    if (size >= (2 << 20)) {
+        ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, flags | MAP_HUGETLB, -1, 0);
+        if (ptr != MAP_FAILED)
+            return ptr;
+        // Fall back to regular pages if huge pages unavailable
+    }
+#endif
 
-    ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED | MAP_NONBLOCK | MAP_POPULATE, -1, 0);
+    ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, flags, -1, 0);
 
     if (ptr == MAP_FAILED)
         return NULL;