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

base/process/process_metrics_linux.cc

Index: base/process/process_metrics_linux.cc
diff --git a/base/process/process_metrics_linux.cc b/base/process/process_metrics_linux.cc
index adca7c5ee23bd53914342cffd2aab166402fe920..8b87aa772832bc03045a76ab62e0a718dc730285 100644
--- a/base/process/process_metrics_linux.cc
+++ b/base/process/process_metrics_linux.cc
@@ -48,20 +48,12 @@ static uint64 ReadFileToUint64(const FilePath file) {
 }
 #endif
 
-// Read /proc/<pid>/status and return the value for |field|, or 0 on failure.
-// Only works for fields in the form of "Field: value kB".
-size_t ReadProcStatusAndGetFieldAsSizeT(pid_t pid, const std::string& field) {
-  std::string status;
-  {
-    // Synchronously reading files in /proc does not hit the disk.
-    ThreadRestrictions::ScopedAllowIO allow_io;
-    FilePath stat_file = internal::GetProcPidDir(pid).Append("status");
-    if (!ReadFileToString(stat_file, &status))
-      return 0;
-  }
-
+// Parse the contents of status file and return the value of the field
+// requested.
+size_t ParseProcStatsAndGetFieldAsSizeT(const char* status_contents,

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

Just use StringPiece instead of const char* ? Then you can pass in a std::string
or const char*, without needing to do .c_str().

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

changed to string

+                                        const std::string& field) {
   StringPairs pairs;
-  SplitStringIntoKeyValuePairs(status, ':', '\n', &pairs);
+  SplitStringIntoKeyValuePairs(status_contents, ':', '\n', &pairs);
   TrimKeyValuePairs(&pairs);
   for (size_t i = 0; i < pairs.size(); ++i) {
     const std::string& key = pairs[i].first;
@@ -85,6 +77,35 @@ size_t ReadProcStatusAndGetFieldAsSizeT(pid_t pid, const std::string& field) {
   return 0;
 }
 
+// Read /proc/<pid>/status and return the value for |field|, or 0 on failure.
+// Only works for fields in the form of "Field: value kB".
+size_t ReadProcStatusAndGetFieldAsSizeT(pid_t pid, const std::string& field) {
+  std::string status;
+  {
+    // Synchronously reading files in /proc does not hit the disk.
+    ThreadRestrictions::ScopedAllowIO allow_io;
+    FilePath stat_file = internal::GetProcPidDir(pid).Append("status");
+    if (!ReadFileToString(stat_file, &status))
+      return 0;
+  }
+  return ParseProcStatsAndGetFieldAsSizeT(status.c_str(), field);
+}
+
+// Read file descriptor passed file descritor of /proc/<pid>/status and return
+// the value for |field|, or 0 on failure.
+// Only works for fields in the form of "Field: value kB".
+size_t ReadProcStatusFdAndGetFieldAsSizeT(PlatformFile proc_status_fd,

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

/proc/<pid>/status isn't that big, right? Why bother passing the fd and not just
the contents? I can see using a fd for smaps, which IIRC, is quite large.

[ssid, 2015/10/07 09:12:14]

yes, I moved the reading part to other file and not the api takes string.

+                                          const std::string& field) {
+  const size_t kMaxStatFileSize = 1 << 12;

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

Easier to just write 4096?

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

Done.

+  char status_data[kMaxStatFileSize];
+  status_data[0] = '\0';
+  lseek(proc_status_fd, 0, SEEK_SET);

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

Check return value?

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

Done.

+  ReadFromFD(proc_status_fd, status_data, kMaxStatFileSize);

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

Ditto, check this return value in place of the next line.

[ssid, 2015/10/07 09:12:14]

Done.

+  if (strlen(status_data) == 0)
+    return 0;
+  return ParseProcStatsAndGetFieldAsSizeT(status_data, field);
+}
+
 #if defined(OS_LINUX)
 // Read /proc/<pid>/sched and look for |field|. On succes, return true and
 // write the value for |field| into |result|.
@@ -393,6 +414,14 @@ bool ProcessMetrics::GetWorkingSetKBytesStatm(WorkingSetKBytes* ws_usage)
   return ret;
 }
 
+size_t ProcessMetrics::GetWorkingSetSize(int proc_status_fd) const {
+  return ReadProcStatusFdAndGetFieldAsSizeT(proc_status_fd, "VmRSS") * 1024;
+}
+
+size_t ProcessMetrics::GetPeakWorkingSetSize(int proc_status_fd) const {
+  return ReadProcStatusFdAndGetFieldAsSizeT(proc_status_fd, "VmHWM") * 1024;
+}
+
 size_t GetSystemCommitCharge() {
   SystemMemoryInfoKB meminfo;
   if (!GetSystemMemoryInfo(&meminfo))