Paging - Performance

Performance

The backing store for a virtual memory operating system is typically many orders of magnitude slower than RAM. Additionally, using mechanical storage devices introduces delay, several milliseconds for a harddisk. Therefore it is desirable to reduce or eliminate swapping, where practical. Some operating systems offer settings to influence the kernel's decisions.

  1. Linux offers the /proc/sys/vm/swappiness parameter, which changes the balance between swapping out runtime memory, as opposed to dropping pages from the system page cache.
  2. Windows 2000, XP, and Vista offer the DisablePagingExecutive registry setting, which controls whether kernel-mode code and data can be eligible for paging out.
  3. Mainframe computers frequently used head-per-track disk drives or drums for page and swap storage to eliminate seek time, and several technologies to have multiple concurrent requests to the same device in order to reduce rotational latency.
  4. Flash memory has a finite number of erase-write cycles, (see Limitations of flash memory), and the smallest amount of data that can be erased at once might be very large (128 KiB for an Intel X25-M SSD ), seldom coinciding with pagesize. Therefore, flash memory may wear out quickly if used as swap space under tight memory conditions. On the attractive side, flash memory is practically delayless compared to harddisks, and not volatile as RAM chips. Schemes like ReadyBoost and Intel Turbo Memory are made to exploit these characteristics.

Many Unix-like operating systems (for example AIX, Linux and Solaris) allow using multiple storage devices for swap space in parallel, to increase performance.

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