Do not realloc if size is in the same sizeclass

src/override/malloc.cc

@@ -80,14 +80,17 @@ extern "C"
         "Calling realloc on pointer that is not to the start of an allocation");
     }
 #endif
-    if (size <= SNMALLOC_NAME_MANGLE(malloc_usable_size)(ptr))
+    size_t sz = SNMALLOC_NAME_MANGLE(malloc_usable_size)(ptr);
+    // Keep the current allocation if the given size is in the same sizeclass.
+    if (sz == sizeclass_to_size(size_to_sizeclass(size)))
       return ptr;
 
     void* p = SNMALLOC_NAME_MANGLE(malloc)(size);
     if (p != nullptr)
     {
       assert(p == Alloc::external_pointer<Start>(p));
-      memcpy(p, ptr, size);
+      sz = (std::min)(size, sz);
+      memcpy(p, ptr, sz);
       SNMALLOC_NAME_MANGLE(free)(ptr);
     }
     return p;