WIP: Num of WB-unprotected objs in eBPF timeline

Show the number of WB-unprotected objects before and after processin the
WB-unprotected object list in the eBPF timeline.

Author: wks

mmtk/src/weak_proc.rs

@@ -440,8 +440,9 @@ impl GCWork<Ruby> for UpdateWbUnprotectedObjectsList {
         );
 
         let old_objects = std::mem::take(&mut *objects);
+        let old_size = old_objects.len();
 
-        debug!("Updating {} WB-unprotected objects", old_objects.len());
+        debug!("Updating {old_size} WB-unprotected objects");
 
         for object in old_objects {
             if object.is_reachable() {
@@ -458,7 +459,10 @@ impl GCWork<Ruby> for UpdateWbUnprotectedObjectsList {
             }
         }
 
-        debug!("Retained {} live WB-unprotected objects.", objects.len());
+        let new_size = objects.len();
+        debug!("Retained {new_size} live WB-unprotected objects.");
+
+        probe!(mmtk_ruby, update_wb_unprotected_objects_list, old_size, new_size);
     }
 }
 

tools/tracing/timeline/capture_ruby.bt

@@ -63,3 +63,9 @@ usdt:$MMTK:mmtk_ruby:process_obj_free_candidates {
         printf("process_obj_free_candidates,meta,%d,%lu,%lu,%lu\n", tid, nsecs, arg0, arg1);
     }
 }
+
+usdt:$MMTK:mmtk_ruby:update_wb_unprotected_objects_list {
+    if (@enable_print) {
+        printf("update_wb_unprotected_objects_list,meta,%d,%lu,%lu,%lu\n", tid, nsecs, arg0, arg1);
+    }
+}

tools/tracing/timeline/visualize_ruby.py

@@ -125,3 +125,13 @@ def enrich_meta_extra(log_processor, name, tid, ts, gc, wp, args):
                         "diff": new_candidates - old_candidates,
                     },
                 }
+
+            case "update_wb_unprotected_objects_list":
+                before, after = [int(x) for x in args[0:2]]
+                wp["args"] |= {
+                    "wb_unprotected_objects": {
+                        "before": before,
+                        "after": after,
+                        "diff": after - before,
+                    },
+                }