From 75bb2bcf8da2da259ae9987972066293687af204 Mon Sep 17 00:00:00 2001
From: Xiaolong Peng <xlpeng@amazon.com>
Date: Tue, 2 Jun 2026 20:41:40 -0700
Subject: [PATCH] Prefer larger region when retaining

---
 .../share/gc/shenandoah/shenandoahPartitionAllocator.cpp      | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/hotspot/share/gc/shenandoah/shenandoahPartitionAllocator.cpp b/src/hotspot/share/gc/shenandoah/shenandoahPartitionAllocator.cpp
index 0674fb2cfb3..560fff81518 100644
--- a/src/hotspot/share/gc/shenandoah/shenandoahPartitionAllocator.cpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahPartitionAllocator.cpp
@@ -155,8 +155,10 @@ HeapWord* ShenandoahPartitionAllocator<PARTITION>::allocate_in(ShenandoahHeapReg
     if (_retained_region == r) {
       _retained_region = nullptr;
     }
-  } else if (_retained_region == nullptr) {
+  } else if (_retained_region == nullptr || _retained_region->free() < r->free()) {
     // Region still has usable capacity — retain for next allocation.
+    // Prefer whichever has more free space so a small retained region doesn't starve
+    // out a larger fresh one.
     _retained_region = r;
   }