tools/deadlock: Add an option to set the maximum number of stack traces

Commit 77f5252 ("tools/deadlock: support specifies maxnum of threads
and edge cases (iovisor#3455)") allow to set the maximum number of threads
and edge cases to be able to reduce the memory usage of the deadlock
tool. It however let the size of the map of stack traces fixed. It's
current size, 640k (actually rounded up to 1M) takes 1Gb of vmalloced
kernel memory.

This patch adds an option to make the maximum number of stack traces
user defined. It also set the default value to 64k, in line with the
current default for the number of edge cases and threads.

It fix the following issue on system with limited memory ressources:
could not open bpf map: stack_traces, error: Cannot allocate memory
Traceback (most recent call last):
  File "/tmp/./deadlock.py", line 577, in <module>
    main()
  File "/tmp/./deadlock.py", line 489, in main
    bpf = BPF(text=text)
  File "/usr/lib/python3.9/site-packages/bcc/__init__.py", line 479, in __init__
    raise Exception("Failed to compile BPF module %s" % (src_file or "<text>"))
Exception: Failed to compile BPF module <text>

Signed-off-by: Jerome Marchand <[email protected]>

tools/deadlock.c

@@ -60,7 +60,7 @@ struct thread_created_leaf_t {
 BPF_HASH(thread_to_parent, u32, struct thread_created_leaf_t);
 
 // Stack traces when threads are created and when mutexes are locked/unlocked.
-BPF_STACK_TRACE(stack_traces, 655360);
+BPF_STACK_TRACE(stack_traces, MAX_TRACES);
 
 // The first argument to the user space function we are tracing
 // is a pointer to the mutex M held by thread T.

tools/deadlock.py

@@ -467,6 +467,13 @@ def main():
  help='Specifies the maximum number of edge cases that can be recorded. '
  'default 65536. Note. 88 bytes per edge case.'
  )
+ parser.add_argument(
+ '-s', '--stacktraces', type=int, default=65536,
+ help='Specifies the maximum number of stack traces that can be recorded. '
+ 'This number is rounded up to the next power of two.'
+ 'default 65536. Note. 1 kbytes vmalloced per stack trace.'
+ )
+
  args = parser.parse_args()
  if not args.binary:
  try:
@@ -479,6 +486,7 @@ def main():
  text = f.read()
  text = text.replace('MAX_THREADS', str(args.threads));
  text = text.replace('MAX_EDGES', str(args.edges));
+ text = text.replace('MAX_TRACES', str(args.stacktraces));
  bpf = BPF(text=text)
 
  # Trace where threads are created