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In computer operating systems, memory paging (or swapping on some Unix-like systems) is a memory management scheme by which a computer stores and retrieves data from secondary storage [a] for use in main memory. [1] In this scheme, the operating system retrieves data from secondary storage in same-size blocks called pages.
In operating systems, memory management is the function responsible for managing the computer's primary memory. [1]: 105–208 The memory management function keeps track of the status of each memory location, either allocated or free. It determines how memory is allocated among competing processes, deciding which gets memory, when they receive ...
A 68451 MMU, which could be used with the Motorola 68010. A memory management unit (MMU), sometimes called paged memory management unit (PMMU), [1] is a computer hardware unit that examines all memory references on the memory bus, translating these requests, known as virtual memory addresses, into physical addresses in main memory.
Thrashing is when the CPU performs 'productive' work less and 'swapping' work more. The overall memory access time may increase since the higher level memory is only as fast as the next lower level in the memory hierarchy. [2] The CPU is busy swapping pages so much that it cannot respond to users' programs and interrupts as much as required.
In computer operating systems, demand paging (as opposed to anticipatory paging) is a method of virtual memory management. In a system that uses demand paging, the operating system copies a disk page into physical memory only when an attempt is made to access it and that page is not already in memory (i.e., if a page fault occurs).
If present in memory and not privately modified the physical page is shared with file cache or buffer. Shared memory acquired through shm_open. The tmpfs in-memory filesystem; written to swap when paged out. The file cache including; written to the underlying block storage (possibly going through the buffer, see below) when paged out.
By reducing the I/O activity caused by paging requests, virtual memory compression can produce overall performance improvements. The degree of performance improvement depends on a variety of factors, including the availability of any compression co-processors, spare bandwidth on the CPU, speed of the I/O channel, speed of the physical memory, and the compressibility of the physical memory ...
Linux tmpfs (previously known as shm fs) [6] is based on the ramfs code used during bootup and also uses the page cache, but, unlike ramfs, it supports swapping out less-used pages to swap space, as well as filesystem size and inode limits to prevent out-of-memory situations (defaulting to half of physical RAM and half the number of RAM pages ...