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The method the operating system uses to select the page frame to reuse, which is its page replacement algorithm, is important to efficiency. The operating system predicts the page frame least likely to be needed soon, often through the least recently used (LRU) algorithm or an algorithm based on the program's working set. To further increase ...
Similarly, a page frame is the smallest fixed-length contiguous block of physical memory into which memory pages are mapped by the operating system. [ 1 ] [ 2 ] [ 3 ] A transfer of pages between main memory and an auxiliary store, such as a hard disk drive , is referred to as paging or swapping.
Each VM has a separate shadow page table and the hypervisor is in charge of managing them. While shadow page tables are faster than double translation, they are still expensive compared to not running in a virtual machine: every time a guest updates its page tables, it requires the hypervisor to also manage changes in the shadow tables.
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).
To use virtual 8086 mode, an operating system sets up a virtual 8086 mode monitor, which is a program that manages the real-mode program and emulates or filters access to system hardware and software resources. The monitor must run at privilege level 0 and in protected mode. Only the 8086 program runs in VM86 mode and at privilege level 3.
The first-in, first-out (FIFO) page replacement algorithm is a low-overhead algorithm that requires little bookkeeping on the part of the operating system. The idea is obvious from the name – the operating system keeps track of all the pages in memory in a queue, with the most recent arrival at the back, and the oldest arrival in front.
An ideal pre-paging scheme would mask large majority of network faults, although its performance depends upon the memory access pattern of the VM's workload. Post-copy sends each page exactly once over the network whereas pre-copy can transfer the same page multiple times if the page is dirtied repeatedly at the source during migration.
The Guest Additions for Windows, Linux, Solaris, OpenSolaris, and OS/2 guests include a special video-driver that increases video performance and includes additional features, such as automatically adjusting the guest resolution when resizing the VM window [38] and desktop composition via virtualized WDDM drivers.