xo-alloc2: ++ documentation + threshold size for THP feature

include/xo/alloc2/print.hpp

@@ -0,0 +1,34 @@
+/** @file print.hpp
+*
+ *  @author Roland Conybeare, Dec 2025
+ **/
+
+#pragma once
+
+#include "AllocError.hpp"
+#include <xo/indentlog/print/tag.hpp>
+#include <iostream>
+
+namespace xo {
+    namespace mm {
+        inline std::ostream &
+        operator<<(std::ostream & os, const error & x) {
+            os << AllocError::error_description(x);
+            return os;
+        }
+
+        inline std::ostream &
+        operator<<(std::ostream & os, const AllocError & x) {
+            os << "<AllocError"
+               << xtag("error", x.error_)
+               << xtag("seq", x.error_seq_)
+               << xtag("req_z", x.request_z_)
+               << xtag("commit_z", x.committed_z_)
+               << xtag("resv_z", x.reserved_z_)
+               << ">";
+            return os;
+        }
+    }
+}
+
+/* end print.hpp */