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How Virtual Memory Works from HowStuffWorks.com (in fact explains only swapping concept, and not virtual memory concept) Linux swap space management (outdated, as the author admits) Guide On Optimizing Virtual Memory Speed (outdated) Virtual Memory Page Replacement Algorithms; Windows XP: How to manually change the size of the virtual memory ...
KSM performs memory deduplication by scanning through main memory for physical pages that have identical content, and identifies the virtual pages that are mapped to those physical pages. It leaves one page unchanged, and re-maps each duplicate page to point to the same physical page, after which it releases the extra physical pages for re-use.
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.
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 ...
The startup function startup_32() for the kernel (also called the swapper or process 0) establishes memory management (paging tables and memory paging), detects the type of CPU and any additional functionality such as floating point capabilities, and then switches to non-architecture specific Linux kernel functionality via a call to start ...
Pages in the page cache modified after being brought in are called dirty pages. [5] Since non-dirty pages in the page cache have identical copies in secondary storage (e.g. hard disk drive or solid-state drive), discarding and reusing their space is much quicker than paging out application memory, and is often preferred over flushing the dirty pages into secondary storage and reusing their space.
The MMU detects the page fault, but the operating system's kernel handles the exception by making the required page accessible in the physical memory or denying an illegal memory access. Valid page faults are common and necessary to increase the amount of memory available to programs in any operating system that uses virtual memory, such as ...
The main difference between System V shared memory (shmem) and memory mapped I/O (mmap) is that System V shared memory is persistent: unless explicitly removed by a process, it is kept in memory and remains available until the system is shut down. mmap'd memory is not persistent between application executions (unless it is backed by a file).