[memory-infra] Implement PollFastMemoryTotal in ProcessMetricsMemoryDumpProvider.

components/tracing/common/process_metrics_memory_dump_provider.cc

Index: components/tracing/common/process_metrics_memory_dump_provider.cc
diff --git a/components/tracing/common/process_metrics_memory_dump_provider.cc b/components/tracing/common/process_metrics_memory_dump_provider.cc
index d2c00c347f0db3f7f9b13286e2af3edc4ac089b3..1ecb35314722e50ed092d8b84ad8e2a7739b2cfb 100644
--- a/components/tracing/common/process_metrics_memory_dump_provider.cc
+++ b/components/tracing/common/process_metrics_memory_dump_provider.cc
@@ -155,6 +155,29 @@ uint32_t ReadLinuxProcSmapsFile(FILE* smaps_file,
   }
   return num_valid_regions;
 }
+
+int OpenStatmFile(base::ProcessId process) {

[Primiano Tucci (use gerrit), 2016/12/15 15:00:02]

Since you kept the full SetFastPollingEnabled(bool) signature, at this point I
think you can remove this funciton and move this code into the "bool = true"
branch of SetFastPollingEnabled, so your code in
ProcessMetricsMemoryDumpProvider::PollFastMemoryTotal will look like:

...
if (fast_polling_statm_fd_ == -1)
  SetFastPollingEnabled(true);
...

[ssid, 2016/12/16 03:16:41]

Done.

+  std::string name =
+      "/proc/" +
+      (process == base::kNullProcessId ? "self" : base::IntToString(process)) +
+      "/statm";
+  return open(name.c_str(), O_RDONLY);
+}
+
+bool GetResidentSizesFromStatmFile(int fd,
+                                   uint64_t* resident_bytes,
+                                   uint64_t* shared_bytes) {
+  lseek(fd, 0, SEEK_SET);
+  char line[kMaxLineSize];
+  int res = read(fd, line, kMaxLineSize);

[Primiano Tucci (use gerrit), 2016/12/15 15:00:02]

if you do this, then here you have to pass kMaxLineSize - 1.
THere is a subtle bug (though very unrealistic) here: if read manages to fill
the buffer, and hence return kMaxLineSize, line 175 will be an out of bound
access  ;-)

[ssid, 2016/12/16 03:16:41]

Done.

+  if (res <= 0)
+    return false;
+  line[res] = '\0';
+  int num_scanned =
+      sscanf(line, "%*s %" SCNu64 " %" SCNu64, resident_bytes, shared_bytes);
+  return num_scanned == 2;
+}
+
 #endif  // defined(OS_LINUX) || defined(OS_ANDROID)
 
 std::unique_ptr<base::ProcessMetrics> CreateProcessMetrics(
@@ -211,6 +234,7 @@ void ProcessMetricsMemoryDumpProvider::RegisterForProcess(
       new ProcessMetricsMemoryDumpProvider(process));
   base::trace_event::MemoryDumpProvider::Options options;
   options.target_pid = process;
+  options.is_fast_polling_supported = true;
   base::trace_event::MemoryDumpManager::GetInstance()->RegisterDumpProvider(
       metrics_provider.get(), "ProcessMemoryMetrics", nullptr, options);
   bool did_insert =
@@ -229,9 +253,8 @@ void ProcessMetricsMemoryDumpProvider::RegisterForProcess(
 void ProcessMetricsMemoryDumpProvider::UnregisterForProcess(
     base::ProcessId process) {
   auto iter = g_dump_providers_map.Get().find(process);
-  if (iter == g_dump_providers_map.Get().end()) {
+  if (iter == g_dump_providers_map.Get().end())
     return;
-  }
   base::trace_event::MemoryDumpManager::GetInstance()
       ->UnregisterAndDeleteDumpProviderSoon(std::move(iter->second));
   g_dump_providers_map.Get().erase(iter);
@@ -241,9 +264,16 @@ ProcessMetricsMemoryDumpProvider::ProcessMetricsMemoryDumpProvider(
     base::ProcessId process)
     : process_(process),
       process_metrics_(CreateProcessMetrics(process)),
-      is_rss_peak_resettable_(true) {}
+      is_rss_peak_resettable_(true) {
+#if defined(OS_LINUX) || defined(OS_ANDROID)
+  fast_polling_statm_fd_ = -1;
+#endif
+}
 
-ProcessMetricsMemoryDumpProvider::~ProcessMetricsMemoryDumpProvider() {}
+ProcessMetricsMemoryDumpProvider::~ProcessMetricsMemoryDumpProvider() {
+  // Clear files in case polling was not disabled yet.
+  SetFastMemoryPollingEnabled(false);
+}
 
 // Called at trace dump point time. Creates a snapshot of the memory maps for
 // the current process.
@@ -309,4 +339,36 @@ bool ProcessMetricsMemoryDumpProvider::DumpProcessTotals(
   return true;
 }
 
+void ProcessMetricsMemoryDumpProvider::PollFastMemoryTotal(
+    uint64_t* memory_total) {
+  *memory_total = 0;
+#if defined(OS_LINUX) || defined(OS_ANDROID)
+  if (fast_polling_statm_fd_ == -1)
+    fast_polling_statm_fd_ = OpenStatmFile(process_);
+  if (fast_polling_statm_fd_ < 0)
+    return;
+
+  uint64_t rss = 0, shared = 0;
+  if (!GetResidentSizesFromStatmFile(fast_polling_statm_fd_, &rss, &shared))
+    return;
+
+  // When adding total for child processes, do not include "shared" since it
+  // will be included in the current processes' total.
+  *memory_total = (process_ == base::kNullProcessId ? rss : rss - shared) *
+                  base::GetPageSize();
+#else
+  *memory_total = process_metrics_->GetWorkingSetSize();
+#endif
+}
+
+void ProcessMetricsMemoryDumpProvider::SetFastMemoryPollingEnabled(
+    bool enabled) {
+#if defined(OS_LINUX) || defined(OS_ANDROID)
+  if (!enabled && fast_polling_statm_fd_ >= 0) {
+    close(fast_polling_statm_fd_);
+    fast_polling_statm_fd_ = -1;
+  }
+#endif
+}
+
 }  // namespace tracing