demand paging


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demand paging

[də′mand ‚pā·jiŋ]
(computer science)
The characteristic of a virtual memory system which retrieves only that part of a user's program which is required during execution.

demand paging

(memory management)
A kind of virtual memory where a page of memory will be paged in if an attempt is made to access it and it is not already present in main memory. This normally involves a memory management unit which looks up the virtual address in a page map to see if it is paged in. If it is not then the operating system will page it in, update the page map and restart the failed access. This implies that the processor must be able to recover from and restart a failed memory access or must be suspended while some other mechanism is used to perform the paging.

Paging in a page may first require some other page to be moved from main memory to disk ("paged out") to make room. If this page has not been modified since it was paged in, it can simply be reused without writing it back to disk. This is determined from the "modified" or "dirty" flag bit in the page map. A replacement algorithm or policy is used to select the page to be paged out, often this is the least recently used (LRU) algorithm.

Prepaging is generally more efficient than demand paging.

demand paging

Copying a page of program code from disk into memory when required by the program.
References in periodicals archive ?
Application-controlled demand paging for out-of-corevisualization.
The demand paging variant of post-copy is the simplest and slowest option.
Any major faults incurred by the VM can be serviced concurrently over the network via demand paging. Active push avoids transferring pages that have already been faulted in by the target VM.
Red Bend Software, a provider of mobile software management technology, announced on Tuesday (16 October) support for the latest available Symbian OS release, Symbian OS v9.4, with Demand Paging.
These include the choice of page size, the role of prepaging as compared with demand paging, and the exploitation of techniques for improving the locality of information, so that fewer pages need to be loaded into high-speed memory.