Thrashing and working set model in Operating Systems - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the sentence to define thrashing.

Operating Systems

Thrashing occurs when a system spends most of its time [1] pages rather than executing processes.

Drag options to blanks, or click blank then click option'

Aswapping

Bloading

Cwriting

Dallocating

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'loading' because it sounds similar to swapping.

Thrashing happens when the system spends too much time swapping pages in and out of memory instead of running actual processes.

2fill in blank

medium

Complete the sentence to explain the working set model.

Operating Systems

The working set model tracks the set of pages a process has used in the last [1] time units.

Drag options to blanks, or click blank then click option'

Arandom

Bfixed

Crecent

Dinfinite

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'fixed' because it sounds like a set size.

The working set model focuses on the pages a process has used recently to decide which pages to keep in memory.

3fill in blank

hard

Fix the error in the sentence about thrashing.

Operating Systems

Thrashing happens when the CPU is mostly idle due to [1] page faults.

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Aexcessive

Brandom

Cno

Dfew

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'few' because it seems less severe.

Thrashing is caused by excessive page faults, which keep the CPU busy handling memory instead of running processes.

4fill in blank

hard

Fill both blanks to describe the working set window and its purpose.

Operating Systems

The working set window is a [1] of time used to determine the [2] of pages a process needs.

Drag options to blanks, or click blank then click option'

Afixed interval

Bnumber

Cset

Dvariable size

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'variable size' because it sounds flexible.

The working set window is a fixed interval of time used to find the set of pages a process currently needs in memory.

5fill in blank

hard

Fill all three blanks to complete the explanation of thrashing prevention.

Operating Systems

To prevent thrashing, the system must [1] the number of [2] and ensure the [3] fits in memory.

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Alimit

Bprocesses

Cworking set

Dincrease

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing 'increase' instead of 'limit' for the first blank.

Preventing thrashing involves limiting the number of processes and making sure each process's working set fits in memory.

Practice

1. What is thrashing in operating systems?

easy

A. A system running multiple programs efficiently

B. A process running without any memory

C. A method to speed up CPU processing

D. Excessive paging causing slow system performance

Solution

1. Step 1: Understand the meaning of thrashing

   Thrashing happens when the system spends too much time swapping pages in and out of memory instead of executing processes.

2. Step 2: Identify the effect of thrashing

   This excessive paging slows down the computer significantly, reducing performance.

3. Final Answer:

   Excessive paging causing slow system performance -> Option D

4. Quick Check:

   Thrashing = Excessive paging slowing system [OK]

Hint: Thrashing means too much swapping slows the computer [OK]

Common Mistakes:

• Confusing thrashing with normal multitasking
• Thinking thrashing speeds up the CPU
• Believing thrashing means no memory usage

2. Which of the following best describes the working set of a process?

easy

A. Pages never accessed by the process

B. All pages in the system memory

C. Pages recently used by the process

D. Pages swapped out to disk

Solution

1. Step 1: Define working set

   The working set is the collection of pages a process has used recently and needs to run efficiently.

2. Step 2: Identify correct description

   Pages recently used by the process fit this definition, unlike all pages or swapped pages.

3. Final Answer:

   Pages recently used by the process -> Option C

4. Quick Check:

   Working set = Recently used pages [OK]

Hint: Working set means pages used recently by process [OK]

Common Mistakes:

• Thinking working set includes all system pages
• Confusing working set with swapped out pages
• Assuming working set is pages never accessed

3. Consider a system where a process's working set size suddenly grows beyond available memory. What is the most likely outcome?

medium

A. Thrashing will occur, slowing down the system

B. The process will run faster due to more pages

C. The system will ignore the extra pages

D. The process will terminate immediately

Solution

1. Step 1: Analyze working set growth impact

   If the working set grows beyond available memory, the system must swap pages frequently to keep up.

2. Step 2: Identify system behavior

   This frequent swapping causes thrashing, which slows down the system instead of speeding it up.

3. Final Answer:

   Thrashing will occur, slowing down the system -> Option A

4. Quick Check:

   Working set too big = Thrashing slows system [OK]

Hint: Too big working set causes thrashing and slowdown [OK]

Common Mistakes:

• Assuming more pages always improve speed
• Believing system ignores memory limits
• Thinking process ends immediately without warning

4. A system is experiencing thrashing. Which change would best reduce thrashing?

medium

A. Increase the working set size of all processes

B. Reduce the number of processes competing for memory

C. Decrease the CPU speed

D. Disable paging completely

Solution

1. Step 1: Understand cause of thrashing

   Thrashing happens when too many processes compete for limited memory, causing excessive paging.

2. Step 2: Identify best solution

   Reducing the number of processes competing for memory lowers paging demand and reduces thrashing.

3. Final Answer:

   Reduce the number of processes competing for memory -> Option B

4. Quick Check:

   Less competition = less thrashing [OK]

Hint: Fewer processes competing reduces thrashing [OK]

Common Mistakes:

• Increasing working set size worsens thrashing
• Decreasing CPU speed does not fix memory issues
• Disabling paging causes system failure

5. A system uses the working set model to manage memory. If a process's working set is 100 pages but only 80 pages fit in memory, what should the system do to avoid thrashing?

hard

A. Swap out some pages from the process's working set

B. Increase the process's working set size to 120 pages

C. Allow the process to run with only 80 pages and swap frequently

D. Terminate the process immediately

Solution

1. Step 1: Analyze working set vs memory size

   The process needs 100 pages to run well, but only 80 pages fit in memory, causing potential thrashing.

2. Step 2: Determine best memory management action

   Swapping out some pages from the working set or adjusting memory allocation helps keep the working set within limits and avoids thrashing.

3. Final Answer:

   Swap out some pages from the process's working set -> Option A

4. Quick Check:

   Adjust working set to fit memory to avoid thrashing [OK]

Hint: Adjust working set size to fit memory to prevent thrashing [OK]

Common Mistakes:

• Increasing working set size worsens thrashing
• Allowing frequent swaps causes thrashing
• Terminating process is last resort, not first