diff --git a/uppsrc/Core/HeapImp.h b/uppsrc/Core/HeapImp.h
index d3c32adca..dcb103e22 100644
--- a/uppsrc/Core/HeapImp.h
+++ b/uppsrc/Core/HeapImp.h
@@ -283,7 +283,7 @@ struct Heap : BlkHeap<HugeHeapDetail, 4096> {
 	int   HugeFree(void *ptr);
 	bool  HugeTryRealloc(void *ptr, size_t count);
 
-	static int Ksz(int k) {
+	static int Ksz(int k) { // small block size classes
 		static int sz[] = {
 		//  0   1   2   3    4    5    6    7    8    9    10   11
 			32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384,
@@ -384,7 +384,7 @@ struct Heap : BlkHeap<HugeHeapDetail, 4096> {
 	static Heap   aux;    // Single global auxiliary heap to store orphans and global list of free pages
 
 	static size_t huge_4KB_count; // total number of 4KB pages in small/large/huge blocks
-	static int    free_4KB; // empty 4KB pages
+	static int    free_4KB; // number of empty 4KB pages (linked in aux.empty)
 	static size_t big_size; // blocks >~64KB
 	static size_t big_count;
 	static size_t sys_size;  // blocks allocated directly from system (included in big too)
@@ -424,6 +424,7 @@ struct Heap : BlkHeap<HugeHeapDetail, 4096> {
 	void *Allok(int k);
 	void  Free(void *ptr, Page *page, int k);
 	void  Free(void *ptr, int k);
+	void  Free4KB(int k, Page *page);
 
 	static bool FreeSmallEmpty(int size4KB, int count = INT_MAX);
 
diff --git a/uppsrc/Core/heap.cpp b/uppsrc/Core/heap.cpp
index fea80b4c9..f68487258 100644
--- a/uppsrc/Core/heap.cpp
+++ b/uppsrc/Core/heap.cpp
@@ -144,10 +144,7 @@ void Heap::Shutdown()
 		if(empty[i]) {
 			ASSERT(empty[i]->freelist);
 			ASSERT(empty[i]->active == 0);
-			empty[i]->heap = &aux;
-			empty[i]->next = aux.empty[i];
-			aux.empty[i] = empty[i];
-			free_4KB++;
+			Free4KB(i, empty[i]);
 			LLOG("Orphan empty " << (void *)empty[i]);
 		}
 	}
diff --git a/uppsrc/Core/sheap.cpp b/uppsrc/Core/sheap.cpp
index 4a98dd9a3..5675685ca 100644
--- a/uppsrc/Core/sheap.cpp
+++ b/uppsrc/Core/sheap.cpp
@@ -184,28 +184,35 @@ void Heap::FreeK(void *ptr, Page *page, int k)
 		page->Unlink();
 		if(this == &aux) {
 			LLOG("...is aux " << asString(free_4KB));
-			page->next = empty[k];
-			empty[k] = page;
-			free_4KB++;
+			Mutex::Lock __(mutex);
+			Free4KB(k, page);
 		}
 		else {
 			if(empty[k]) { // Keep one hot empty page per klass in thread, put rest to 'aux' global storage
-				LLOG("Global free " << k << " " << (void *)empty[k]);
 				Mutex::Lock __(mutex);
-				if(free_4KB < max_free_spages) { // only keep max_free_spages, release if more
-					empty[k]->heap = &aux;
-					empty[k]->next = aux.empty[k];
-					aux.empty[k] = empty[k];
-					free_4KB++;
-				}
-				else
-					aux.HugeFree(empty[k]);
+				Free4KB(k, empty[k]); // Free current hot page to reserve/huge
 			}
-			empty[k] = page;
+			empty[k] = page; // this empty page is now hot
 		}
 	}
 }
 
+void Heap::Free4KB(int k, Page *page)
+{ // put empty 4KB to aux reserve or back to huge blocks if the reserve is full
+	LLOG("Global Free4KB " << k << " " << (void *)empty);
+	if(free_4KB < max_free_spages) { // only keep max_free_spages, release if more
+		page->heap = &aux;
+		page->next = aux.empty[k];
+		aux.empty[k] = page;
+		free_4KB++;
+		LLOG("Reserve 4KB " << asString(free_4KB));
+	}
+	else {
+		aux.HugeFree(page);
+		LLOG("HugeFree 4KB " << asString(free_4KB));
+	}
+}
+
 force_inline
 void Heap::Free(void *ptr, Page *page, int k)
 {