In the process of debugging 7066129 the customer found another user who is also seeing C-heap growth.
They have narrowed it down to ThreadService::find_deadlocks_at_safepoint
> gdb) info leak 4
> 240 bytes leaked in 10 blocks (0.68% of all bytes leaked)
> These range in size from 24 to 24 bytes and are allocated
> #0 0x9fffffff7e944fa2 in os::malloc(unsigned long) at
> #1 0x9fffffff7cff5a22 in CHeapObj::operator new(unsigned long) at
> #2 0x9fffffff7ed95a
> <http://ukpatch.uksr.hp.com:32080/search/patch?patch=ff7ed95a>32 in
> ThreadService::find_deadlocks_at_safepoint(bool) at
> #3 0x9fffffff7ee7f822 in VM_FindDeadlocks::doit()
See comments for the testcase.