Virtual memory

operating system level memory management technique

computer hardware unit having all memory references passed through itself, primarily performing the translation of virtual memory addresses to physical addresses

memory management scheme by which a computer stores and retrieves data from secondary storage for use in main memory

Copy-on-write (COW), also called implicit sharing or shadowing, is a resource-management technique used in programming to manage shared data efficiently. Instead of copying data right away when multiple programs use it, the same data is shared between programs until one tries to modify it. If no changes are made, no private copy is created, saving resources. A copy is only made when needed, ensuring each program has its own version when modifications occur. This technique is commonly applied to memory, files, and data structures.

memory cache that is used to reduce the time taken to access a user memory location; part of the chip’s memory-management unit

memory management feature

data structure that maps virtual addresses with physical addresses

when a running program accesses a memory page that is not currently mapped by the MMU into the virtual address space of a process

phenomenon that when a computer's virtual memory subsystem is in a constant state of paging, rapidly exchanging data in memory for data on disk, to the exclusion of most application-level processing

algorithm in an OS that decides which memory pages to page out (swap out, write to disk) when a requested page is not in memory (page fault) and a free page cannot be used to satisfy the allocation (because there are too few or none)

fixed-length contiguous block of virtual memory

zram, formerly called compcache, is a Linux kernel module for creating a compressed block device in RAM, i.e. a RAM disk with on-the-fly disk compression. The block device created with zram can then be used for swap or as a general-purpose RAM disk. The two most common uses for zram are for the storage of temporary files () and as a swap device. Initially, zram had only the latter function, hence the original name "compcache" ("compressed cache"). When empty, zram block device allocates about 0.1% of its size.

representation of memory address

segment of virtual memory that has been assigned a direct byte-for-byte correlation with some portion of a file or file-like resource

programming method

set of ranges of virtual addresses

hardening technique in Linux kernel

address at which an item appears to reside from the perspective of an executing application program

zswap is a Linux kernel feature that provides a compressed write-back cache for swapped pages, as a form of virtual memory compression. Instead of moving memory pages to a swap device when they are to be swapped out, zswap performs their compression and then stores them into a memory pool dynamically allocated in the system RAM. Later writeback to the actual swap device is deferred or even completely avoided, resulting in a significantly reduced I/O for Linux systems that require swapping; the tradeoff is the need for additional CPU cycles to perform the compression.

Algorithm for caching data

collection of data in memory that a process is expected to actually touch in some workload