2 files changed, 30 insertions, 19 deletions

diff --git a/src/core/lib/channel/channel_trace.cc b/src/core/lib/channel/channel_trace.cc
index cfb2faba51..3227fe53a1 100644
--- a/src/core/lib/channel/channel_trace.cc
+++ b/src/core/lib/channel/channel_trace.cc
@@ -48,31 +48,37 @@ ChannelTrace::TraceEvent::TraceEvent(Severity severity, grpc_slice data,
       timestamp_(grpc_millis_to_timespec(grpc_core::ExecCtx::Get()->Now(),
                                          GPR_CLOCK_REALTIME)),
       next_(nullptr),
-      referenced_entity_(std::move(referenced_entity)) {}
+      referenced_entity_(std::move(referenced_entity)) {
+  memory_usage_ = sizeof(TraceEvent) + grpc_slice_memory_usage(data);
+}
 
 ChannelTrace::TraceEvent::TraceEvent(Severity severity, grpc_slice data)
     : severity_(severity),
       data_(data),
       timestamp_(grpc_millis_to_timespec(grpc_core::ExecCtx::Get()->Now(),
                                          GPR_CLOCK_REALTIME)),
-      next_(nullptr) {}
+      next_(nullptr) {
+  memory_usage_ = sizeof(TraceEvent) + grpc_slice_memory_usage(data);
+}
 
 ChannelTrace::TraceEvent::~TraceEvent() { grpc_slice_unref_internal(data_); }
 
-ChannelTrace::ChannelTrace(size_t max_events)
+ChannelTrace::ChannelTrace(size_t max_event_memory)
     : num_events_logged_(0),
-      list_size_(0),
-      max_list_size_(max_events),
+      event_list_memory_usage_(0),
+      max_event_memory_(max_event_memory),
       head_trace_(nullptr),
       tail_trace_(nullptr) {
-  if (max_list_size_ == 0) return;  // tracing is disabled if max_events == 0
+  if (max_event_memory_ == 0)
+    return;  // tracing is disabled if max_event_memory_ == 0
   gpr_mu_init(&tracer_mu_);
   time_created_ = grpc_millis_to_timespec(grpc_core::ExecCtx::Get()->Now(),
                                           GPR_CLOCK_REALTIME);
 }
 
 ChannelTrace::~ChannelTrace() {
-  if (max_list_size_ == 0) return;  // tracing is disabled if max_events == 0
+  if (max_event_memory_ == 0)
+    return;  // tracing is disabled if max_event_memory_ == 0
   TraceEvent* it = head_trace_;
   while (it != nullptr) {
     TraceEvent* to_free = it;
@@ -93,25 +99,27 @@ void ChannelTrace::AddTraceEventHelper(TraceEvent* new_trace_event) {
     tail_trace_->set_next(new_trace_event);
     tail_trace_ = tail_trace_->next();
   }
-  ++list_size_;
-  // maybe garbage collect the end
-  if (list_size_ > max_list_size_) {
+  event_list_memory_usage_ += new_trace_event->memory_usage();
+  // maybe garbage collect the tail until we are under the memory limit.
+  while (event_list_memory_usage_ > max_event_memory_) {
     TraceEvent* to_free = head_trace_;
+    event_list_memory_usage_ -= to_free->memory_usage();
     head_trace_ = head_trace_->next();
     Delete<TraceEvent>(to_free);
-    --list_size_;
   }
 }
 
 void ChannelTrace::AddTraceEvent(Severity severity, grpc_slice data) {
-  if (max_list_size_ == 0) return;  // tracing is disabled if max_events == 0
+  if (max_event_memory_ == 0)
+    return;  // tracing is disabled if max_event_memory_ == 0
   AddTraceEventHelper(New<TraceEvent>(severity, data));
 }
 
 void ChannelTrace::AddTraceEventWithReference(
     Severity severity, grpc_slice data,
     RefCountedPtr<BaseNode> referenced_entity) {
-  if (max_list_size_ == 0) return;  // tracing is disabled if max_events == 0
+  if (max_event_memory_ == 0)
+    return;  // tracing is disabled if max_event_memory_ == 0
   // create and fill up the new event
   AddTraceEventHelper(
       New<TraceEvent>(severity, data, std::move(referenced_entity)));
@@ -162,8 +170,8 @@ void ChannelTrace::TraceEvent::RenderTraceEvent(grpc_json* json) const {
 }
 
 grpc_json* ChannelTrace::RenderJson() const {
-  if (!max_list_size_)
-    return nullptr;  // tracing is disabled if max_events == 0
+  if (max_event_memory_ == 0)
+    return nullptr;  // tracing is disabled if max_event_memory_ == 0
   grpc_json* json = grpc_json_create(GRPC_JSON_OBJECT);
   grpc_json* json_iterator = nullptr;
   if (num_events_logged_ > 0) {
@@ -174,7 +182,7 @@ grpc_json* ChannelTrace::RenderJson() const {
       json_iterator, json, "creationTimestamp",
       gpr_format_timespec(time_created_), GRPC_JSON_STRING, true);
   // only add in the event list if it is non-empty.
-  if (num_events_logged_ > 0) {
+  if (head_trace_ != nullptr) {
     grpc_json* events = grpc_json_create_child(json_iterator, json, "events",
                                                nullptr, GRPC_JSON_ARRAY, false);
     json_iterator = nullptr;
diff --git a/src/core/lib/channel/channel_trace.h b/src/core/lib/channel/channel_trace.h
index 94fea20b45..0e9ce5f648 100644
--- a/src/core/lib/channel/channel_trace.h
+++ b/src/core/lib/channel/channel_trace.h
@@ -37,7 +37,7 @@ class BaseNode;
 // https://github.com/grpc/proposal/blob/master/A14-channelz.md
 class ChannelTrace {
  public:
-  ChannelTrace(size_t max_events);
+  ChannelTrace(size_t max_event_memory);
   ~ChannelTrace();
 
   enum Severity {
@@ -92,6 +92,8 @@ class ChannelTrace {
     TraceEvent* next() const { return next_; }
     void set_next(TraceEvent* next) { next_ = next; }
 
+    size_t memory_usage() { return memory_usage_; }
+
    private:
     Severity severity_;
     grpc_slice data_;
@@ -99,6 +101,7 @@ class ChannelTrace {
     TraceEvent* next_;
     // the tracer object for the (sub)channel that this trace event refers to.
     RefCountedPtr<BaseNode> referenced_entity_;
+    size_t memory_usage_;
   };  // TraceEvent
 
   // Internal helper to add and link in a trace event
@@ -106,8 +109,8 @@ class ChannelTrace {
 
   gpr_mu tracer_mu_;
   uint64_t num_events_logged_;
-  size_t list_size_;
-  size_t max_list_size_;
+  size_t event_list_memory_usage_;
+  size_t max_event_memory_;
   TraceEvent* head_trace_;
   TraceEvent* tail_trace_;
   gpr_timespec time_created_;