diff --git a/imperative/src/impl/physical_tensor.cpp b/imperative/src/impl/physical_tensor.cpp
index 2fb7201093d5c62a87d69a48d30be8d950acbd20..3a895afe849a18145721f314d437b11983553bd3 100644
--- a/imperative/src/impl/physical_tensor.cpp
+++ b/imperative/src/impl/physical_tensor.cpp
@@ -125,6 +125,7 @@ public:
         size_t size;
         BlobPtr blob;
 
+        Entry() = default;
         Entry(const dt_byte* ptr, size_t size_, BlobPtr blob_)
                 : data(new dt_byte[size_]), size(size_), blob(blob_) {
             memcpy(data.get(), ptr, size);
@@ -136,6 +137,8 @@ public:
         }
     };
 
+    using KV = std::pair<uint64_t, Entry>;
+
     bool check(const HostTensorND& hv) {
         auto&& layout = hv.layout();
         auto&& span = layout.span();
@@ -190,7 +193,7 @@ public:
     }
 
     std::mutex mtx;
-    size_t hwm = 1024, lwm = 512, max_bytes = TensorShape::MAX_NDIM * 8, window = 65536;
+    const size_t hwm = 1024, lwm = 512, max_bytes = TensorShape::MAX_NDIM * 8, window = 65536;
 
 private:
     void maybe_collect_g0() {
@@ -200,25 +203,37 @@ private:
         }
     }
     void maybe_collect_g1() {
-        if (g1.size() <= hwm) return;
+        if (g1.size() < hwm) return;
 
-        using KV = std::pair<uint64_t, Entry>;
-        std::vector<KV> tmp;
-        tmp.reserve(g1.size());
+        tmp.clear();
         for (auto&& kv : g1) {
             tmp.emplace_back(kv.first, std::move(kv.second));
         }
         std::nth_element(tmp.begin(), tmp.begin() + lwm, tmp.end(), [](const KV& lhs, const KV& rhs) {
                 return lhs.second.hitcnt > rhs.second.hitcnt;
             });
+        tmp.resize(lwm);
         g1.clear();
         for (auto&& kv : tmp) {
             kv.second.hitcnt = 0;
             g1.emplace(std::move(kv));
         }
     }
+
+    // g0: records blobs which have been seen at least once (within a window)
+    // g0b: backup of g0
+    // g1: records the most frequently used blobs which have been seen at least
+    // twice. When `g1.size() == hwm`, it will be refreshed and only the top
+    // `lhw` frequently used blobs will be kept.
     std::unordered_set<uint64_t> g0, g0b;
     std::unordered_map<uint64_t, Entry> g1;
+    std::vector<KV> tmp;
+
+public:
+    ConstTensorCache() {
+        g0.reserve(window), g0b.reserve(window);
+        g1.reserve(hwm), tmp.reserve(hwm);
+    }
 };
 
 struct MultiCNConstTensorCache : CompNodeDepedentObject {