Check the option before aggregating live bytes data. Panic if the opt…

…ion is enabled on malloc space. (#1250)

We see failures
[here](https://github.com/mmtk/mmtk-core/actions/runs/12193674159/job/34020377988?pr=1248)
in OpenJDK tests.

```
[2024-12-06T07:09:55Z INFO  mmtk::memory_manager] Initialized MMTk with MarkSweep (FixedHeapSize(54525952))
[2024-12-06T07:09:55Z WARN  mmtk::memory_manager] The feature 'extreme_assertions' is enabled. MMTk will run expensive run-time checks. Slow performance should be expected.
===== DaCapo fop starting =====
[2024-12-06T07:10:07Z INFO  mmtk::util::heap::gc_trigger] [POLL] MallocSpace: Triggering collection (13313/13312 pages)
thread '<unnamed>' panicked at /home/runner/work/mmtk-core/mmtk-core/mmtk-openjdk/repos/mmtk-core/src/policy/marksweepspace/malloc_ms/global.rs:158:9:
internal error: entered unreachable code
stack backtrace:
   0: rust_begin_unwind
             at /rustc/aedd173a2c086e558c2b66d3743b344f977621a7/library/std/src/panicking.rs:647:5
   1: core::panicking::panic_fmt
             at /rustc/aedd173a2c086e558c2b66d3743b344f977621a7/library/core/src/panicking.rs:72:14
   2: core::panicking::panic
             at /rustc/aedd173a2c086e558c2b66d3743b344f977621a7/library/core/src/panicking.rs:144:5
   3: <mmtk::policy::marksweepspace::malloc_ms::global::MallocSpace<VM> as mmtk::policy::space::Space<VM>>::common
             at ./repos/mmtk-core/src/policy/marksweepspace/malloc_ms/global.rs:158:9
   4: mmtk::policy::space::Space::get_descriptor
             at ./repos/mmtk-core/src/policy/space.rs:332:9
   5: mmtk::mmtk::MMTK<VM>::aggregate_live_bytes_in_last_gc::{{closure}}
             at ./repos/mmtk-core/src/mmtk.rs:542:29
   6: <mmtk::plan::marksweep::global::MarkSweep<VM> as mmtk::plan::global::HasSpaces>::for_each_space
             at ./repos/mmtk-core/src/plan/marksweep/global.rs:31:10
   7: mmtk::mmtk::MMTK<VM>::aggregate_live_bytes_in_last_gc
             at ./repos/mmtk-core/src/mmtk.rs:540:9
   8: <mmtk::scheduler::gc_work::Release<C> as mmtk::scheduler::work::GCWork<<C as mmtk::scheduler::work::GCWorkContext>::VM>>::do_work
             at ./repos/mmtk-core/src/scheduler/gc_work.rs:162:13
   9: mmtk::scheduler::work::GCWork::do_work_with_stat
             at ./repos/mmtk-core/src/scheduler/work.rs:45:9
  10: mmtk::scheduler::worker::GCWorker<VM>::run
             at ./repos/mmtk-core/src/scheduler/worker.rs:255:13
  11: mmtk::memory_manager::start_worker
             at ./repos/mmtk-core/src/memory_manager.rs:491:5
  12: start_worker
             at ./mmtk/src/api.rs:214:9
  13: _ZN6Thread8call_runEv
             at ./repos/openjdk/src/hotspot/share/runtime/thread.cpp:402:12
  14: thread_native_entry
             at ./repos/openjdk/src/hotspot/os/linux/os_linux.cpp:826:19
  15: <unknown>
  16: <unknown>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
fatal runtime error: failed to initiate panic, error 5
```

The issue is that `aggregate_live_bytes_in_last_gc` was not guarded by
the condition that the option `count_live_bytes_in_gc` is enabled. So it
was executed in our tests.

The function accesses the space descriptor through `CommonSpace` and
`MallocSpace` does not use `CommonSpace`, thus we see the panic. This PR
adds a check before calling `aggregate_live_bytes_in_last_gc`. When the
option is not enabled, we will not call the function.

This PR also adds a panic for `MallocSpace`. If `count_live_bytes` is
turned on, we simply panic, as we cannot provide live bytes vs total
page stats for `MallocSpace`.

src/policy/marksweepspace/malloc_ms/global.rs

@@ -274,6 +274,11 @@ impl<VM: VMBinding> MallocSpace<VM> {
     }
 
     pub fn new(args: crate::policy::space::PlanCreateSpaceArgs<VM>) -> Self {
+        if *args.options.count_live_bytes_in_gc {
+            // The implementation of counting live bytes needs a SpaceDescriptor which we do not have for MallocSpace.
+            // Besides we cannot meaningfully measure the live bytes vs total pages for MallocSpace.
+            panic!("count_live_bytes_in_gc is not supported by MallocSpace");
+        }
         MallocSpace {
             phantom: PhantomData,
             active_bytes: AtomicUsize::new(0),

src/scheduler/gc_work.rs

@@ -154,12 +154,14 @@ impl<C: GCWorkContext + 'static> GCWork<C::VM> for Release<C> {
             debug_assert!(result.is_ok());
         }
 
-        let live_bytes = mmtk
-            .scheduler
-            .worker_group
-            .get_and_clear_worker_live_bytes();
-        *mmtk.state.live_bytes_in_last_gc.borrow_mut() =
-            mmtk.aggregate_live_bytes_in_last_gc(live_bytes);
+        if *mmtk.get_options().count_live_bytes_in_gc {
+            let live_bytes = mmtk
+                .scheduler
+                .worker_group
+                .get_and_clear_worker_live_bytes();
+            *mmtk.state.live_bytes_in_last_gc.borrow_mut() =
+                mmtk.aggregate_live_bytes_in_last_gc(live_bytes);
+        }
     }
 }