[Monotone-devel] memory leak in Botan::Pipe?

[Nathaniel Smith]

We were noticing some serious resource usage problems in 'mtn
checkout' on large trees, and the evidence seems to be pointing to
some sort of problem in Botan.  On a checkout of h:net.venge.monotone,
a medium-sized tree, valgrind reports ~5 megabytes of leaked data, all
of data allocated at line 189 of Botan's pipe.cpp:

void Pipe::find_endpoints(Filter* f)
   {
   for(u32bit j = 0; j != f->total_ports(); ++j)
      if(f->next[j] && !dynamic_cast<SecureQueue*>(f->next[j]))
         find_endpoints(f->next[j]);
      else
         {
         SecureQueue* q = new SecureQueue;       // <---- right here
         f->next[j] = q;
         outputs->add(q);
         }
   }

The application code that (eventually) calls find_endpoints and
triggers the leaks is (with comments and asserts removed):

  {
    ofstream file(tmp.as_external().c_str(),
                  ios_base::out | ios_base::trunc | ios_base::binary);
    Botan::Pipe pipe(new Botan::DataSink_Stream(file));
    pipe.process_msg(dat());
  }

This doesn't _look_ like we're doing anything wrong to me... I don't
understand the memory handling strategy that Pipe is using, though, so
I don't know where the actual bug is.

This problem was initially encountered when doing tests on a giant
repository (100,000+ files, 1+ gigabytes), where monotone mysterously
ended with hundreds of megabytes of resident memory, presumably
because of this leak; so this is a relatively serious problem.

(This massive leak also triggered pathological behavior in Botan's
memory management routines -- somewhere over 97% of cpu time was
being spent in Pooling_Allocator::deallocate.  Glibc's default
heap routines were able to scale to this load easily, though, when I
tried swapping in a trivial malloc-based allocator -- is there really
any reason to use Pooling_Allocator for unlocked memory?)

-- Nathaniel

-- 
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