Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Memory Leaks Presentation Matthew Welch Thomas Adam Andrew Woods

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Introduction What memory leakage is; How it is handled under: –Windows; –Linux; –MAC OS; Methods that the OS uses to handle memory leaks; Various third-party applications that handle memory leakage; Our own conclusions about how to handle memory leakage;

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Memory Leakage Continual allocation of memory to a process; Memory is never freed; System becomes unresponsive;

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Windows Virtual Memory ; Process creation allows entire swap file; Dynamic Link Libraries (dll's) are usually the culprit;

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Linux Linux kernel 2.2.X onwards defines Out Of Memory (OOM-killer); Processes therefore aren't allowed to consume the entire VM; Self-preservation of the kernel; Parent/Child hierarchy of processes; Uninterruptible sleep means the parent process must die;

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Mac OS Mac OS 6 had poor memory design features; Memory allocated via the concept of pointers; Fragmentation; MacOS 9 onwards uses techniques from Linux; Memory leaks mostly confined to applications;

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Introduction to Memory Recovery Plugging memory leaks is very similar to doing Garbage Collection. Not normally done at the OS level, but at the sandbox / virtual machine level. Time and performance issues.

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Reference Counting References additions/deletions are kept track of. When a block has no references, it may be deleted. Very easy to get into a situation where memory is not recovered.

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Mark and Sweep Two stage process Mark – System goes from known memory references (program stack, global variables, and CPU registers) Sweep – Any areas not marked are freed for re-use.

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Stop and Copy Similar to Mark and Sweep, Works against fragmentation also Only instead of Sweep, allocated data is copied to a different area

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Reference Searching Search of *all* memory held by the program. Considers that any data held in memory could be a memory reference. Quite slow. Single pass. Can be done repeatedly for better performance. May not recover all lost memory – a conservative approach.

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Smart Pointers and Custom Libraries Not an algorithm, more of a programming technique. Available for many languages, especially C, C++ Normal pointers are ‘operator overloaded’ Prevent dangling pointers, lost objects. Can provide automatic memory freeing. Override the standard memory allocation functions to provide more functionality.

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Final Note State of the art Garbage Collection is still improving in terms of: Execution time Incremental and interruptible Approaching suitability for near-real-time systems.

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Taking a look at three products that are meant to make memory management easier.

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Why The Need For A Third Party Program Windows Poorly programmed applications Memory leaks Types of memory management software available –Programming Environment –Application Environment

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Programs Available Linux Environment –Dynamic Leak Check –Qps –Memtester –Asmem Windows Environment –MemDefrag 2 –MemOptimizer –MemMonster –Release RAM –RamCleaner –Clean Ram –SuperRam –Alto Memory Booster –MemTurbo

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch MemMonster Rating for memMonster Price£25 Value for money4 File Size KB785 KB Ease of use3 Flexibility/Functions3 Appearance on screen3 Increase in performance300% Operating SystemWindows 98/ME/NT/2K/XP and 2003 DeveloperMagellass Corp Rating 1 out of 53

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Alto Memory Booster Rating for Alto memory Price£11.10 Value for money2 File Size KB1,573 KB Ease of use3 Flexibility/Functions2 Appearance on screen5 Increase in performance200% Operating SystemWindows 98/ME/NT/2000 and XP DeveloperAlto Software Rating 1 out of 53

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch MemTurbo Rating for memTurbo Price£29.95 Value for money4 File Size KB796 KB Ease of use4 Flexibility/Functions4 Appearance on screen5 Increase in performance200% Operating SystemWindows 95/98/NT 4.0/2000 and XP DeveloperSoftwareOnline Rating 1 out of 54

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Conclusion Comparing & Contrasting Software Programs Reviewed memTurbomemMonsterAlto memory Pros  Aim at a more professional due to Advanced capabilities  Reliability and robust  Free support for end-user  Good help guide  Navigation & GUI to a high quality and standard Pros  Most middle range of the three packages both in features, functions and price  Easy to configure  Offers settings for disk caching  Good value for money Pros  Familiarity, especially on the desktop (icons)  Windows configuration wizard for auto-set-up  Less training needed for users  Easy to get started  Most cost effective Cons  Least cost effective  More training required Cons  Exaggerated claims for performance (not 300% in trail review)  Navigation is poor & not clearly defined Cons  Lacking features and advanced functions  Not as an effective memory management software program compared to memTurbo or memMonster  Double the file size compared to memTurbo & memMonster  Questionable reliability and efficiency Top range package for middle to advance user Middle range package for novice to beginner Lower range package for beginner

Saturday, 10 October 2015 Andrew Woods, Thomas Adam, Matthew Welch Towards a Leak Free OS? First Line: ‘Mark and Sweep’ Second Line: Restricting the number of memory pages that the process may consume. Why? Effectiveness: These methods combined should effectively: –Prevent memory leakage, by recovering memory from leaky processes –For runaway processes, terminating them. Disadvantages –Timing –Interruptions for GC