![]() ![]() MAXDATA of 0x00000000 is the default setting, which means for a 32-bit process, the heap and stack share a single 256MB memory segment (the 0x2 segment). In this case, we see that ' leaktest' is a 32-bit process with a MAXDATA value of 0x00000000. The MAXDATA value can be checked outside of dbx, with the ' dump' command: # dump -Xany -ov. In this case, the data limit is set to unlimited, so there is no constriction on usable heap memory there. RLIMIT_DATA: (unlimited) (unlimited) bytes RLIMIT_FSIZE: (unlimited) (unlimited) bytes Rlimit name: rlimit_cur rlimit_max (units) The process limits can be checked inside of dbx with 'proc rlimit': (dbx) proc rlimit You'll also need to be aware of process limits and the process MAXDATA value in order to determine if the core dump was likely due to running out of memory on the heap. To determine if this amount of memory usage is excessive, you'll have to be aware of what the expected memory usage is for the process that you are examining some processes may need to allocate and hold a large amount of memory. Also, since the start of this process, 255 memory allocations have been made, and they are all currently active - none of them have been freed. That tells me that the process currently has ~256MB of memory allocated on the heap - looking at 'bytes held' - and there is not much left on the free space tree that can be used for new allocations. Statistical Report on the Malloc Subsystem: ![]() Inside dbx, run the ' malloc' subcommand to check memory usage statistics: (dbx) malloc coreĠx0000fc04 warning: Unable to access address 0xfc04 from core Running that, it cores rather quickly, and then I load the core in dbx: # dbx. The program simply allocates 1MB repeatedly without freeing it: void func1() In this example, I have a program called ' leaktest' which is designed to leak memory. If you already suspect a particular process has a leak, monitor it specifically with ' svmon -P -O summary=basic,unit=MB'.Īnother method to use, if a core dump has occurred, is to look at the malloc statistics in dbx. Monitor process memory usage with ' svmon -P -O summary=basic,unit=MB' to display memory usage of all processes, and make note of any processes that might be using an unexpected amount of memory. The first step in diagnosing a memory leak is to recognize that you are experiencing a leak. Using this unnecessarily causes more memory usage due to the overhead needed to check for overflows. That is a setting that is only needed when diagnosing buffer overwrites or overreads, and does not apply to memory leak detection. MALLOCTYPE=debug is deprecated, and it is equivalent to the setting MALLOCDEBUG=catch_overflow. Older documentation may suggest that MALLOCTYPE=debug should be set during the debug process however, it is not needed and should not be used when performing memory leak diagnosis. This could result in core dumps, unexpected behavior of the process, or could cause a performance issue if the excessive memory usage results in the system paging out memory to paging space. ![]() This becomes a problem if the process is a long-running process, like a daemon - the excess memory usage builds up over time. A memory leak is a condition where a process allocates memory, but does not free it when it is done with it. ![]()
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