Merge #14693: test_node: get_mem_rss fixups

fa9ed38 test_node: get_mem_rss fixups (MarcoFalke)

Pull request description:

  Follow up to #14522:

  * Fix math (Memory usage increase relative to previous memory usage, not final memory usage)
  * remove `shell=True`
  * assert that the node is running
  * Make it work on BSD-like systems

Tree-SHA512: fc1b4f88173914b6cb6373655cffd781044a0c146339e3fa90da03b197faa20954567a77335965b857d29d27f32661698b6a0340f0c616f643b8c4510cd360c2

test/functional/test_framework/test_node.py

@@ -118,22 +118,19 @@ def get_deterministic_priv_key(self):
  def get_mem_rss(self):
  """Get the memory usage (RSS) per `ps`.
 
- If process is stopped or `ps` is unavailable, return None.
+ Returns None if `ps` is unavailable.
  """
- if not (self.running and self.process):
- self.log.warning("Couldn't get memory usage; process isn't running.")
- return None
+ assert self.running
 
  try:
  return int(subprocess.check_output(
- "ps h -o rss {}".format(self.process.pid),
- shell=True, stderr=subprocess.DEVNULL).strip())
+ ["ps", "h", "-o", "rss", "{}".format(self.process.pid)],
+ stderr=subprocess.DEVNULL).split()[-1])
 
- # Catching `Exception` broadly to avoid failing on platforms where ps
- # isn't installed or doesn't work as expected, e.g. OpenBSD.
+ # Avoid failing on platforms where ps isn't installed.
  #
  # We could later use something like `psutils` to work across platforms.
- except Exception:
+ except (FileNotFoundError, subprocess.SubprocessError):
  self.log.exception("Unable to get memory usage")
  return None
 
@@ -308,7 +305,7 @@ def assert_memory_usage_stable(self, perc_increase_allowed=0.03):
  self.log.warning("Unable to detect memory usage (RSS) - skipping memory check.")
  return
 
- perc_increase_memory_usage = 1 - (float(before_memory_usage) / after_memory_usage)
+ perc_increase_memory_usage = (after_memory_usage / before_memory_usage) - 1
 
  if perc_increase_memory_usage > perc_increase_allowed:
  self._raise_assertion_error(