[tools] Add tools/memory/rss.py to sample RSS usage

Similar to how `time COMMAND` measures time, `rss.py COMMAND` measures
memory consumption, by sampling RSS (Resident Set Size) for the child
process in /proc at a configurable interval (default: every 1ms).

No-Try: true
Change-Id: I381cdd6325fae67944ee96e44ba09dd948d432cd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3971360
Reviewed-by: Matthias Liedtke <mliedtke@chromium.org>
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Matthias Liedtke <mliedtke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83858}

tools/memory/rss.py

@@ -0,0 +1,95 @@
+#!/usr/bin/env python3
+# Copyright 2022 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import subprocess
+import sys
+import time
+
+kDefaultSamplerateSecs = 0.001
+
+
+def PrintHelp(returncode):
+  print(f"""Usage: {sys.argv[0]} [--interval I] [--freq F] [--] COMMAND
+
+Runs COMMAND, and samples its RSS memory usage every I milliseconds (or F \
+times per second).
+Default sample interval is {kDefaultSamplerateSecs * 1000} ms.
+'--' as argument forces all further arguments to be part of COMMAND.
+""")
+  sys.exit(returncode)
+
+
+def Main():
+  # Parse arguments.
+  args = []
+  samplerate_secs = kDefaultSamplerateSecs
+  idx = 1
+  while idx < len(sys.argv):
+    arg = sys.argv[idx]
+    if arg == "--":
+      args += sys.argv[(idx + 1):]
+      break
+    if arg in ("-h", "--help", "help"):
+      PrintHelp(0)
+    elif arg in ("--interval", "-I"):
+      if idx + 1 >= len(sys.argv):
+        PrintHelp(1)
+      samplerate_secs = int(sys.argv[idx + 1]) / 1000
+      idx += 1  # Skip the value.
+    elif arg in ("--freq", "-F"):
+      if idx + 1 >= len(sys.argv):
+        PrintHelp(1)
+      samplerate_secs = 1 / float(sys.argv[idx + 1])
+      idx += 1  # Skip the value.
+    else:
+      # No match for known parameter; assume it's part of the command to run.
+      args.append(arg)
+    idx += 1  # Go to next arg.
+
+  cmd = " ".join(args)
+  print(f"sample rate: {samplerate_secs}")
+  print(f"command: {cmd}")
+
+  # Run the child process and observe it.
+  process = subprocess.Popen(cmd, shell=True)
+  pid = process.pid
+  print(f"pid: {pid}")
+  statusfile = f"/proc/{pid}/status"
+  vmsum = 0
+  observed_max = 0
+  reported_max = 0
+  sample_count = 0
+  while process.poll() is None:
+    with open(statusfile, 'r') as f:
+      for line in f.read().splitlines():
+        if line.startswith("VmRSS"):
+          rss = int(line.split()[1])
+          vmsum += rss
+          if rss > observed_max:
+            observed_max = rss
+        elif line.startswith("VmHWM"):
+          peak = int(line.split()[1])
+          if peak > reported_max:
+            reported_max = peak
+      sample_count += 1
+    time.sleep(samplerate_secs)
+
+  # Report findings.
+  print("\n")
+  # TODO(jkummerow): See if this is accurate enough in practice.
+  walltime = sample_count * samplerate_secs
+  print(f"wall time:    {walltime:.3f} s")  # Sample rate precision!
+  print("")
+  avg = vmsum / sample_count / 1024
+  reported_max /= 1024
+  observed_max /= 1024
+  print(f"average RSS:  {avg:.2f} MB")
+  print(f"reported max: {reported_max:.2f} MB")
+  print(f"observed max: {observed_max:.2f} MB")
+  sys.exit(process.returncode)
+
+
+if __name__ == "__main__":
+  Main()