[GitHub] [arrow] westonpace commented on a change in pull request #12702: ARROW-15062: [C++] Add memory information to current spans

[GitBox <gi...@apache.org>]

westonpace commented on a change in pull request #12702:
URL: https://github.com/apache/arrow/pull/12702#discussion_r834730496



##########
File path: cpp/src/arrow/util/tracing_internal.cc
##########
@@ -184,6 +188,41 @@ opentelemetry::trace::Tracer* GetTracer() {
   return tracer.get();
 }
 
+int parseLine(char* line){
+  // This assumes that a digit will be found and the line ends in " Kb".
+  int i = strlen(line);
+  const char* p = line;
+  while (*p <'0' || *p > '9') p++;
+  line[i-3] = '\0';
+  i = atoi(p);
+  return i;
+}
+
+size_t GetMemoryUsedByProcess() { //Note: this value is in KB!
+  FILE* file = fopen("/proc/self/status", "r");
+  size_t result = -1;
+  char line[128];
+
+  while (fgets(line, 128, file) != NULL){
+    if (strncmp(line, "VmRSS:", 6) == 0){
+      result = parseLine(line);
+      break;
+    }
+  }
+  fclose(file);
+  return result*1000;
+}
+
+size_t GetMemoryUsed() {
+  size_t total_memory_size;
+  size_t used_memory_size;
+  struct sysinfo si;
+  sysinfo(&si);

Review comment:
       There was a portable implementation as part of a PR here: https://github.com/apache/arrow/pull/11426/files#diff-5d7d9a549780da2ec4baba08a43db3e1d524b70d6e8ae4f29cc8bfe831357f9cR178-R199 
   
   We didn't end up pursuing the PR but you might be able to borrow some from that particular function.
   
   That being said, I wonder if it would be more valuable to report `default_memory_pool()->bytes_allocated()`.  `sysinfo` is going to give us statistics on the entire server and `freeram` is sometimes misleading (e.g. if there are a lot of dirty pages then `freeram` could be high while at the same time we might be thrashing swap).




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