From 27dafac7537ebd1963a5be0f8dfb7750fc645d4c Mon Sep 17 00:00:00 2001
From: Xiaolong Peng <xlpeng@amazon.com>
Date: Wed, 21 Jan 2026 15:13:13 -0800
Subject: [PATCH] Remove _active_alloc_region flag and directly use field
 _atomic_top to determine atomic alloc region

---
 .../share/gc/shenandoah/shenandoahHeapRegion.cpp    |  1 -
 .../share/gc/shenandoah/shenandoahHeapRegion.hpp    | 13 ++++---------
 2 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp b/src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp
index 2c6e0140bf1..79bfe389502 100644
--- a/src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp
@@ -90,7 +90,6 @@ ShenandoahHeapRegion::ShenandoahHeapRegion(HeapWord* start, size_t index, bool c
     SpaceMangler::mangle_region(MemRegion(_bottom, _end));
   }
   _recycling.unset();
-  _active_alloc_region.unset();
 }
 
 void ShenandoahHeapRegion::report_illegal_transition(const char *method) {
diff --git a/src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.hpp b/src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.hpp
index b62e545b480..2602c1b1aec 100644
--- a/src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.hpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.hpp
@@ -270,8 +270,6 @@ private:
 
   bool _needs_bitmap_reset;
 
-  ShenandoahSharedFlag _active_alloc_region; // Flag indicates that whether the region is an active alloc region.
-
 public:
   ShenandoahHeapRegion(HeapWord* start, size_t index, bool committed);
 
@@ -563,11 +561,9 @@ public:
 
   inline void set_active_alloc_region() {
     shenandoah_assert_heaplocked();
-    assert(_active_alloc_region.is_unset(), "Must be");
-    // Sync _top to _atomic_top before setting _active_alloc_region flag to prepare for CAS allocation
     assert(atomic_top() == nullptr, "Must be");
+    // Sync _top to _atomic_top to set the region as an active atomic alloc region
     AtomicAccess::release_store(&_atomic_top, top<false>());
-    _active_alloc_region.set();
   }
 
   // Unset a heap region as active alloc region,
@@ -593,13 +589,12 @@ public:
       }
       current_atomic_top = prior_atomic_top;
     }
-    OrderAccess::fence();
-    assert(top<false>() == current_atomic_top, "Value of _atomic_top must have synced to _top.");
-    _active_alloc_region.unset();
+    assert(top<false>() == current_atomic_top, "Value of _atomic_top must have synced to _top");
   }
 
   inline bool is_active_alloc_region() const {
-    return _active_alloc_region.is_set();
+    // region is an active atomic alloc region if the atomic top is set
+    return atomic_top() != nullptr;
   }
 
 private: