DetectingMemoryLeakOnAIX.docVIP

Methods For Identifying Memory Leaks In AIX Systems PAGE  Version 1 – 4/ 8 / 2005  PAGE 13 of  NUMPAGES 13 ? 2005 IBM Corporation Methods for Identifying Memory Leaks in AIX Systems By Barry J. Saad and Harold R. Lee Application memory leaks can be difficult to detect and on modern multi-tasking systems where many applications are running, it can be even more difficult to identify the offending process(es). This paper will explore the reasons for memory leaks, and using the AIX system performance tools, provide a methodology for identifying them to the process level. This paper will consist of four major parts: (1) definition and causes for a memory leak on a system, (2) examining a process heap using svmon and ps, (3) a method for detecting memory leaks on a system, (4) a method for identifying individual processes which have memory leaks. The Causes for Memory Leaks The Jargon File version 4.2.0 defines a memory leak as: memory leak n. An error in a programs dynamic-storeallocation logic that causes it to fail to reclaim discarded memory,leading to eventual collapse due to memory exhaustion. These problems were severe on older machines with small, fixed-size address spaces, and special leak detection tools were commonly written to root them out. With the advent of virtual memory, it is unfortunately easier to be sloppy about wasting a bit of memory (although when you run out of memory on a VM machine, it means youve got a _real_ leak!). Memory is allocated to a processes heap by using the malloc() C library call or in C++ when a class is instantiated by calling a “constructor” which will “set up” the class by allocating the required memory for the class and initializing the members. When the memory is no longer required by the process, it is released for reuse by the free() C library system call or in C++ when the class is “torn down” by calling a “destructor” which will release the memory for reuse. When a process terminates, all of the program’s