Update src/alloc/isolated_alloc.rs

Co-authored-by: Ralf Jung <post@ralfj.de>

Author: nia-e

src/alloc/isolated_alloc.rs

@@ -229,8 +229,9 @@ impl IsolatedAlloc {
                 pinfo.remove(idx);
             }
 
-            // Only 1 page might have been freed after a dealloc, so if it exists,
-            // find it and free it (and adjust the vectors)
+            // This may have been the last allocation on this page. If so, free the entire page.
+            // FIXME: this can lead to threshold effects, we should probably add some form
+            // of hysteresis.
             if pinfo.is_empty() {
                 // SAFETY: `self.page_size` is always a power of 2 and does not overflow an isize
                 let page_layout =