Contents
What is the main role of MMU?
A memory management unit (MMU), sometimes called paged memory management unit (PMMU), is a computer hardware unit having all memory references passed through itself, primarily performing the translation of virtual memory addresses to physical addresses.
What is the role of MMU in translating addresses?
A memory management unit translates addresses between the CPU and physical memory. This translation process is often known as memory mapping because addresses are mapped from a logical space into a physical space. Because modern CPUs typically do not have this limitation, MMUs are used to provide virtual addressing.
How does the MMU work?
The task of the MMU is to abstract the physical memory addresses to one or more virtual address spaces. When the MMU is enabled, the CPU accesses memory via virtual addresses which will be translated by the MMU to physical addresses before sending them on the memory bus. Every CPU core has its own MMU.
What is MMU and TLB?
A translation lookaside buffer (TLB) is a memory cache that is used to reduce the time taken to access a user memory location. It is a part of the chip’s memory-management unit (MMU). This is called a TLB hit.
How does the MMU translate the virtual page offset to the physical page offset?
The MMU now immediately knows what physical memory page to access without the need to look into the global memory. In the example provided in the above diagram, the virtual page number is found in the TLB, and immediately translated to the physical page number. The page offset is passed through as it is not translated.
What thrashing means?
Thrashing is a state in which the CPU performs ‘productive’ work less, and ‘swapping’ more. Thrashing occurs when there are too many pages in memory, and each page refers to another page. The real memory shortens in capacity to have all the pages in it, so it uses ‘virtual memory’.
What is the purpose of page table?
A page table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual addresses and physical addresses.
How the MMU is used to translate a virtual address to a real physical address?
Memory Management Unit
The CPU manages translation of virtual to physical addresses using its Memory Management Unit (MMU). A virtual address is specified as a offset from the start of a memory segment; these segments are used by the kernel and user processes to hold their text, stack, data, and other regions.
How does MMU translate incoming virtual memory to outgoing physical memory?
The MMU is responsible for the translation between virtual memory addresses and physical memory addresses. With vSphere ESXi, a virtual machine’s vCPU will call out to MMU functionality by the Virtual Machine Monitor (VMM) process, or a hardware MMU supported by a vendor specific CPU offloading instruction.
What is cache thrashing?
Cache thrash is caused by an ongoing computer activity that fails to progress due to excessive use of resources or conflicts in the caching system. A key sign of cache thrashing is high CPU usage or a system that seems to be running very slowly. In this case, thrashing can be occurring even if there are no page faults.
How are page faults satisfied by memory swapping?
A minor page fault can be satisfied by sharing pages that are already in memory. Swapping occurs when pages are written to the disk to free memory so that a major page fault can be satisfied. Swap activity is the primary performance concern when it comes to page faults. More servers?
What’s the difference between minor and major page fault?
When the CPU needs to access a page that isn’t in memory it raises a page fault. A major page fault is one that can only be satisfied by accessing the disk. A minor page fault can be satisfied by sharing pages that are already in memory. Swapping occurs when pages are written to the disk to free memory so that a major page fault can be satisfied.
How does a page fault handler work in a computer?
The page fault handler in the operating system merely needs to make the entry for that page in the memory management unit point to the page in memory and indicate that the page is loaded in memory; it does not need to read the page into memory.
How does reducing the number of page faults improve performance?
Optimization of programs and the operating system that reduce the number of page faults improve the performance of the program or even the entire system. The two primary focuses of the optimization effort are reducing overall memory usage and improving memory locality.