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Friday, April 21, 2023 Andrew Woods, Thomas Adam, Matthew Welch
Memory Leaks Presentation
Matthew WelchThomas AdamAndrew Woods
Friday, April 21, 2023 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;
Friday, April 21, 2023 Andrew Woods, Thomas Adam, Matthew Welch
Memory Leakage
• Continual allocation of memory to a process; • Memory is never freed;• System becomes unresponsive;
Friday, April 21, 2023 Andrew Woods, Thomas Adam, Matthew Welch
Windows
• Virtual Memory ;• Process creation allows entire swap file;• Dynamic Link Libraries (dll's) are usually the culprit;
Friday, April 21, 2023 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;
Friday, April 21, 2023 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;
Friday, April 21, 2023 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.
Friday, April 21, 2023 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.
Friday, April 21, 2023 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.
Friday, April 21, 2023 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
Friday, April 21, 2023 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.
Friday, April 21, 2023 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.
Friday, April 21, 2023 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.
Friday, April 21, 2023 Andrew Woods, Thomas Adam, Matthew Welch
Taking a look at three products that are meant to make memory
management easier.
Friday, April 21, 2023 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
Friday, April 21, 2023 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
Friday, April 21, 2023 Andrew Woods, Thomas Adam, Matthew Welch
MemMonster
Rating for memMonster
Price £25
Value for money 4
File Size KB 785 KB
Ease of use 3
Flexibility/Functions 3
Appearance on screen 3
Increase in performance 300%
Operating System Windows 98/ME/NT/2K/XP and 2003
Developer Magellass Corp
Rating 1 out of 5 3
Friday, April 21, 2023 Andrew Woods, Thomas Adam, Matthew Welch
Alto Memory Booster
Rating for Alto memory
Price £11.10
Value for money 2
File Size KB 1,573 KB
Ease of use 3
Flexibility/Functions 2
Appearance on screen 5
Increase in performance 200%
Operating System Windows 98/ME/NT/2000 and XP
Developer Alto Software
Rating 1 out of 5 3
Friday, April 21, 2023 Andrew Woods, Thomas Adam, Matthew Welch
MemTurbo
Rating for memTurbo
Price £29.95
Value for money 4
File Size KB 796 KB
Ease of use 4
Flexibility/Functions 4
Appearance on screen 5
Increase in performance 200%
Operating System Windows 95/98/NT 4.0/2000 and XP
Developer SoftwareOnline
Rating 1 out of 5 4
Friday, April 21, 2023 Andrew Woods, Thomas Adam, Matthew Welch
ConclusionComparing & Contrasting Software Programs Reviewed
memTurbo memMonster Alto 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
Friday, April 21, 2023 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
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