update

Signed-off-by: ylzh10 <[email protected]>

Author: ylzh10

src/address_allocator.rs

@@ -67,22 +67,21 @@ impl AddressAllocator {
     ) -> Result<RangeInclusive> {
         let constraint = Constraint::new(size, alignment, policy)?;
         let allocated = self.interval_tree.allocate(constraint)?;
-        self.used += allocated.len() as usize;
+        self.used.checked_add(allocated.len() as usize).expect("Failed to calculate used memory");
         Ok(allocated)
     }
 
     /// Deletes the specified memory slot or returns `ResourceNotAvailable` if
     /// the node was not allocated before.
     pub fn free(&mut self, key: &RangeInclusive) -> Result<()> {
         self.interval_tree.free(key)?;
-        self.used -= key.len() as usize;
+        self.used.checked_sub(key.len() as usize).expect("Failed to calculate used memory");
         Ok(())
     }
 
     /// Returns the used memory size in this allocator.
-    /// NOTE that due to fragmentations, it's not guaranteed that the next
-    /// allocate() call after querying the used memory can succeed with
-    /// allocating all unused memories and it may still return OOM.
+    /// NOTE that due to fragmentations, not all unused memory may be available
+    /// for next `allocate()` call!
     pub fn used(&self) -> usize {
         self.used
     }