[NOT TO COMMIT YET] Using proc/pid/status file contents to get process metrics in linux.

base/trace_event/process_memory_totals_dump_provider.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/process_memory_totals_dump_provider.h"
 
 #include "base/process/process_metrics.h"
 #include "base/trace_event/process_memory_dump.h"
 #include "base/trace_event/process_memory_totals.h"
 
@@ skipping 37 matching lines @@
     : process_metrics_(CreateProcessMetricsForCurrentProcess()) {
 }
 
 ProcessMemoryTotalsDumpProvider::~ProcessMemoryTotalsDumpProvider() {
 }
 
 // Called at trace dump point time. Creates a snapshot the memory counters for
 // the current process.
 bool ProcessMemoryTotalsDumpProvider::OnMemoryDump(const MemoryDumpArgs& args,
                                                    ProcessMemoryDump* pmd) {
-  const uint64 rss_bytes = rss_bytes_for_testing
-                               ? rss_bytes_for_testing
-                               : process_metrics_->GetWorkingSetSize();
-
+  uint64 rss_bytes;
   uint64 peak_rss_bytes = 0;
 
+  if (UNLIKELY(rss_bytes_for_testing)) {
+    rss_bytes = rss_bytes_for_testing;
+#if defined(OS_LINUX)

[Lei Zhang, 2015/10/06 21:09:00]

I haven't thought about this much, but if there's a way to separate the #ifdefs
from being intertwined with the if-else statements, that would be a lot cleaner.

[ssid, 2015/10/07 09:12:15]

I cannot remove the ifdef totally since proc_status_file makes sense only in
case of linux. I removed the ifdef around the member, but the variable will only
be set in linux / android. This is so that I can move the ifdef here inside the
else instead of having ifdef around else statement.
The inner ifdef cannot be remove since ParseStatus... is defined only in
linux/android.

+  } else if (proc_status_fd.is_valid()) {
+    rss_bytes = process_metrics_->GetWorkingSetSize(proc_status_fd.get());
+    peak_rss_bytes =
+        process_metrics_->GetPeakWorkingSetSize(proc_status_fd.get());
+#endif
+  } else {
+    rss_bytes = process_metrics_->GetWorkingSetSize();
 #if !defined(OS_IOS)
-  peak_rss_bytes = process_metrics_->GetPeakWorkingSetSize();
+    peak_rss_bytes = process_metrics_->GetPeakWorkingSetSize();
+#endif
+  }
+
 #if defined(OS_LINUX) || defined(OS_ANDROID)
   if (kernel_supports_rss_peak_reset) {
     // TODO(ssid): Fix crbug.com/461788 to write to the file from sandboxed
     // processes.
     int clear_refs_fd = open("/proc/self/clear_refs", O_WRONLY);
     if (clear_refs_fd > 0 &&
         WriteFileDescriptor(clear_refs_fd, kClearPeakRssCommand,
                             sizeof(kClearPeakRssCommand))) {
       pmd->process_totals()->set_is_peak_rss_resetable(true);
     } else {
       kernel_supports_rss_peak_reset = false;
     }
     close(clear_refs_fd);
   }
 #endif  // defined(OS_LINUX) || defined(OS_ANDROID)
-#endif  // !defined(OS_IOS)
 
   if (rss_bytes > 0) {
     pmd->process_totals()->set_resident_set_bytes(rss_bytes);
     pmd->process_totals()->set_peak_resident_set_bytes(peak_rss_bytes);
     pmd->set_has_process_totals();
     return true;
   }
 
   return false;
 }
 
 }  // namespace trace_event
 }  // namespace base