I discovered a written explanation of virtual memory on Android phones by Benjamin Zeman. https://www.androidpolice.com/how-virtual-memory-works-on-android/
I appreciated this source because it answered both of the questions in the assignment.
How does virtual memory extend the memory available to applications?- ” In Android, as in other operating systems, a memory address is a way for applications to reference memory locations. Because of virtual memory, these addresses don’t have to correspond to physical locations in the device’s RAM. Instead, Android uses virtual memory to give each application the illusion of having its own large, continuous block of memory by leveraging additional secondary storage space. This allows applications on Android to isolate themselves from one another, providing an additional layer of security and preventing one application from interfering with the memory of another (Zeman, 2024).”
What are the drawbacks of a page fault when a virtual memory page is not resident?- “Page faults: Sometimes, an application can request access to a virtual page that is not currently mapped to a physical page, and a page fault occurs. The operating system has to retrieve the data from zRAM or storage, which can cause a delay.” I had to find out what ‘not resident’ meant. As in many of the new terminologies I am encountering, I have to research the definition.
“The drawbacks of a page fault for a non-resident virtual memory page are performance degradation, as the OS must fetch the page from slower secondary storage (like a hard disk), and potential thrashing, which is a state of excessive page swapping that leads to an unresponsive system. This process introduces significant delays in program execution and can lead to poor CPU utilization, as the processor waits for memory operations to complete (Zeman, 2024).”
I discovered a second written explanation on virtual memory on Android phones by Ayush Chourasia.- https://www.digitaltrends.com/phones/virtual-ram-smartphone-explained/
How does virtual memory extend the memory available to applications?- “How does Virtual RAM work on Android? How does Virtual RAM work? The simple answer is it allocates a certain amount of space from your main storage — so 4GB, 6GB, etc. But, to completely understand the workings of Virtual RAM, we must first understand how memory management on Android works. An Android device is equipped with three kinds of memory — RAM (LPDDR4, LPDDR4x), internal storage (eMMC or UFS), and zRAM, the latter of which is basically a partition inside your RAM that stores low-priority compressed data running in the background. This is done to allow space on your RAM for the app or apps running in the foreground (Chourasia, 2022).”
What are the drawbacks of a page fault when a virtual memory page is not resident?- I searched for hours and could not find a source that both referenced page faults(as I understand them) and virtual memory on Android phones on the same webpage. Thus, though this written source is useful and there are some references to paging it will not be my preferred source. “Pages are defined into two types — “clean pages” and “dirty pages.” Clean pages have an unmodified copy of data saved in the storage, while dirty pages keep a modified copy. An unmodified copy is static data that doesn’t change, while a modified copy is dynamic data that changes every moment. Android can get rid of clean pages when they do not need access to resources, freeing up space in RAM (Chourasia, 2022).”
I preferred my first choice by Benjamin Zeman because while my search term was specific “Virtual memory and page faults on Android phones” the search results gave me the website with the exact information I needed. To describe it, there were subheadings such as; A brief history, Understanding virtual memory through a library analogy, Address vs. physical location, How virtual memory works on Android, Virtual memory terms and processes, Benefits of virtual memory on Android, Performance considerations, Is virtual memory still needed with fast SSDs?, and Optimize your Android with virtual memory.