[memory-infra] Log reasons for memory dump failure

base/trace_event/memory_dump_manager.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/trace_event/memory_dump_manager.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/atomic_sequence_num.h"
@@ skipping 319 matching lines @@
   (*mdp_iter)->disabled = true;
   dump_providers_.erase(mdp_iter);
 }
 
 void MemoryDumpManager::RequestGlobalDump(
     MemoryDumpType dump_type,
     MemoryDumpLevelOfDetail level_of_detail,
     const MemoryDumpCallback& callback) {
   // Bail out immediately if tracing is not enabled at all.
   if (!UNLIKELY(subtle::NoBarrier_Load(&memory_tracing_enabled_))) {
+    VLOG(1) << "Global memory dump failed because " << kTraceCategory

[Primiano Tucci (use gerrit), 2016/06/08 18:00:45]

I'd say s/Global memory dump/memory-infra dump/.
Imagine this shows in the log, more people know what memory-infra is. "GLobal
memory dump" is more obscure, can sound like a crash reporting thing.

[petrcermak, 2016/06/09 09:46:09]

Done.

+            << " tracing category is not enabled";
     if (!callback.is_null())
       callback.Run(0u /* guid */, false /* success */);
     return;
   }
 
   const uint64_t guid =
       TraceLog::GetInstance()->MangleEventId(g_next_guid.GetNext());
 
   // Creates an async event to keep track of the global dump evolution.
   // The |wrapped_callback| will generate the ASYNC_END event and then invoke
@@ skipping 65 matching lines @@
   // Initalizes the ThreadLocalEventBuffer to guarantee that the TRACE_EVENTs
   // in the PostTask below don't end up registering their own dump providers
   // (for discounting trace memory overhead) while holding the |lock_|.
   TraceLog::GetInstance()->InitializeThreadLocalEventBufferIfSupported();
 
   // |dump_thread_| might be destroyed before getting this point.
   // It means that tracing was disabled right before starting this dump.
   // Anyway either tracing is stopped or this was the last hop, create a trace
   // event, add it to the trace and finalize process dump invoking the callback.
   if (!pmd_async_state->dump_thread_task_runner.get()) {
+    VLOG(1)
+        << "Global memory dump failed because dump thread was destroyed before "

[Primiano Tucci (use gerrit), 2016/06/08 18:00:45]

you probably want to make "Global Memory Dump" (or the new suggestion) a
kConstant, so you are guaranteed that you can grep for that constatn in the logs
and they will all start with the same prefix.

[petrcermak, 2016/06/09 09:46:09]

Done.

+        << (pmd_async_state->pending_dump_providers.empty()
+                ? "finalizing memory dump"
+                : pmd_async_state->pending_dump_providers.back().get()->name);
     pmd_async_state->dump_successful = false;
     pmd_async_state->pending_dump_providers.clear();
   }
   if (pmd_async_state->pending_dump_providers.empty())
     return FinalizeDumpAndAddToTrace(std::move(pmd_async_state));
 
   // Read MemoryDumpProviderInfo thread safety considerations in
   // memory_dump_manager.h when accessing |mdpinfo| fields.
   MemoryDumpProviderInfo* mdpinfo =
       pmd_async_state->pending_dump_providers.back().get();
@@ skipping 154 matching lines @@
         TRACE_EVENT_PHASE_MEMORY_DUMP,
         TraceLog::GetCategoryGroupEnabled(kTraceCategory), event_name,
         trace_event_internal::kGlobalScope, dump_guid, pid,
         kTraceEventNumArgs, kTraceEventArgNames,
         kTraceEventArgTypes, nullptr /* arg_values */, &event_value,
         TRACE_EVENT_FLAG_HAS_ID);
   }
 
   bool tracing_still_enabled;
   TRACE_EVENT_CATEGORY_GROUP_ENABLED(kTraceCategory, &tracing_still_enabled);
-  if (!tracing_still_enabled)
+  if (!tracing_still_enabled) {
     pmd_async_state->dump_successful = false;
+    VLOG(1) << "Memory dump failed: Tracing is not enabled any more";

[Primiano Tucci (use gerrit), 2016/06/08 18:00:45]

I'd say here: tracing disabled before the memory dump was completed.

[petrcermak, 2016/06/09 09:46:09]

Done.

+  }
 
   if (!pmd_async_state->callback.is_null()) {
     pmd_async_state->callback.Run(dump_guid, pmd_async_state->dump_successful);
     pmd_async_state->callback.Reset();
   }
 
   TRACE_EVENT_NESTABLE_ASYNC_END0(kTraceCategory, "ProcessMemoryDump",
                                   TRACE_ID_MANGLE(dump_guid));
 }
 
@@ skipping 209 matching lines @@
   if (heavy_dump_rate_ > 0 && periodic_dumps_count_ % heavy_dump_rate_ == 0)
     level_of_detail = MemoryDumpLevelOfDetail::DETAILED;
   ++periodic_dumps_count_;
 
   MemoryDumpManager::GetInstance()->RequestGlobalDump(
       MemoryDumpType::PERIODIC_INTERVAL, level_of_detail);
 }
 
 }  // namespace trace_event
 }  // namespace base