diff --git a/core/box/region_id_v6_box.h b/core/box/region_id_v6_box.h
index 90f21ff6..1753f5da 100644
--- a/core/box/region_id_v6_box.h
+++ b/core/box/region_id_v6_box.h
@@ -122,9 +122,13 @@ void region_id_observe_unregister(uint32_t id);
 // ============================================================================
 
 /// TLS cache for fast lookup (single entry)
+/// Phase V6-HDR-4 P1: page_meta キャッシュ追加
 typedef struct RegionIdTlsCache {
-    uintptr_t last_base;        // Cached region base
-    uintptr_t last_end;         // Cached region end
+    uintptr_t last_base;        // Cached segment base
+    uintptr_t last_end;         // Cached segment end
+    uintptr_t last_page_base;   // Cached page base (for same-page optimization)
+    uintptr_t last_page_end;    // Cached page end
+    SmallPageMetaV6* last_page; // Cached page_meta (direct pointer)
     RegionLookupV6 last_result; // Cached result
 } RegionIdTlsCache;
 
diff --git a/core/region_id_v6.c b/core/region_id_v6.c
index cdc0ce6c..11f7eebd 100644
--- a/core/region_id_v6.c
+++ b/core/region_id_v6.c
@@ -103,20 +103,37 @@ RegionLookupV6 region_id_lookup_v6(void* ptr) {
 
     uintptr_t addr = (uintptr_t)ptr;
 
-    // Phase V6-HDR-3: Check TLS segment registration first (fast path)
+    // Phase V6-HDR-4 P0: Direct page_meta calculation (Double validation 排除)
+    // TLS segment が登録済みかつ範囲内なら、small_page_meta_v6_of() を呼ばずに
+    // 直接 page_meta を計算する。これにより:
+    // - slot->in_use チェックの重複を排除
+    // - small_ptr_in_segment_v6() の重複を排除
+    // - 関数呼び出しオーバーヘッドを削減
     if (g_v6_segment_registered && addr >= g_v6_segment_base && addr < g_v6_segment_end) {
-        // ptr is in this thread's v6 segment - get page_meta
-        SmallPageMetaV6* page = small_page_meta_v6_of(ptr);
-        if (page != NULL) {
-            result.kind = REGION_KIND_SMALL_V6;
-            result.region_id = 1;  // Single TLS segment per thread
-            result.page_meta = page;
+        // Calculate page_idx directly using TLS cached base
+        size_t page_idx = (addr - g_v6_segment_base) >> SMALL_PAGE_V6_SHIFT;
 
-            // Update TLS cache
-            RegionIdTlsCache* cache = region_id_tls_cache_get();
-            cache->last_base = g_v6_segment_base;
-            cache->last_end = g_v6_segment_end;
-            cache->last_result = result;
+        // Bounds check (should always pass if segment is valid)
+        if (likely(page_idx < SMALL_PAGES_PER_SEGMENT)) {
+            SmallPageMetaV6* page = &g_v6_segment->page_meta[page_idx];
+
+            // Minimal validation: only check capacity (page is in use)
+            if (likely(page->capacity > 0)) {
+                result.kind = REGION_KIND_SMALL_V6;
+                result.region_id = 1;
+                result.page_meta = page;
+
+                // Phase V6-HDR-4 P1: Update TLS cache with page-level info
+                RegionIdTlsCache* cache = region_id_tls_cache_get();
+                cache->last_base = g_v6_segment_base;
+                cache->last_end = g_v6_segment_end;
+                // Page-level cache: same-page ptr は page_meta lookup をスキップ可能
+                uintptr_t page_base = g_v6_segment_base + (page_idx << SMALL_PAGE_V6_SHIFT);
+                cache->last_page_base = page_base;
+                cache->last_page_end = page_base + SMALL_PAGE_V6_SIZE;
+                cache->last_page = page;
+                cache->last_result = result;
+            }
         }
         return result;
     }
@@ -144,16 +161,33 @@ RegionLookupV6 region_id_lookup_cached_v6(void* ptr) {
     RegionIdTlsCache* cache = region_id_tls_cache_get();
     uintptr_t addr = (uintptr_t)ptr;
 
-    // TLS cache hit?
+    // Phase V6-HDR-4 P1: Same-page hit optimization
+    // 同一ページ内なら page_meta lookup を完全にスキップ
+    if (addr >= cache->last_page_base && addr < cache->last_page_end &&
+        cache->last_page != NULL && cache->last_page->capacity > 0) {
+        // Same page hit - return cached page_meta directly
+        RegionLookupV6 result = cache->last_result;
+        result.page_meta = cache->last_page;
+        return result;
+    }
+
+    // Segment hit but different page - need to recalculate page_meta
     if (addr >= cache->last_base && addr < cache->last_end &&
         cache->last_result.kind != REGION_KIND_UNKNOWN) {
-        // Cache hit - but still need to get the correct page_meta
-        // for this specific ptr (page_idx may differ)
-        SmallPageMetaV6* page = small_page_meta_v6_of(ptr);
-        if (page) {
-            RegionLookupV6 result = cache->last_result;
-            result.page_meta = page;
-            return result;
+        // Calculate new page_idx
+        size_t page_idx = (addr - cache->last_base) >> SMALL_PAGE_V6_SHIFT;
+        if (likely(page_idx < SMALL_PAGES_PER_SEGMENT && g_v6_segment != NULL)) {
+            SmallPageMetaV6* page = &g_v6_segment->page_meta[page_idx];
+            if (likely(page->capacity > 0)) {
+                RegionLookupV6 result = cache->last_result;
+                result.page_meta = page;
+                // Update page-level cache
+                uintptr_t page_base = cache->last_base + (page_idx << SMALL_PAGE_V6_SHIFT);
+                cache->last_page_base = page_base;
+                cache->last_page_end = page_base + SMALL_PAGE_V6_SIZE;
+                cache->last_page = page;
+                return result;
+            }
         }
     }