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Title: Zram  
Author: World Heritage Encyclopedia
Language: English
Subject: Linux kernel, Virtual memory, Android KitKat, Memory management, Lubuntu
Publisher: World Heritage Encyclopedia


Written in C
Operating system Linux
Type Linux kernel features
License GNU General Public License
Website .orgkernel

zram (also referred to as zRAM) is a module of the Linux kernel, previously called "compcache". zram increases performance by avoiding paging to disk and using a compressed block device in RAM instead, inside which paging takes place until it is necessary to use the swap space on a hard disk drive. Since using RAM is an alternative way to provide swapping on RAM, zram allows Linux to make more use of RAM when swapping/paging is required, especially on older computers with less RAM installed.[1][2]

Despite the cost of RAM being relatively low (as of February 2014), zram still offers advantages for embedded devices, netbooks and similar low-end hardware devices. Such devices usually use flash-based storage which has a limited lifespan due to its nature, so avoiding its usage for providing swap space prevents it from wearing out quickly. Also, using zram results in a significantly reduced I/O for Linux systems that require swapping.[3][4]

zram was merged into the Linux kernel mainline in kernel version 3.14, released on 30 March 2014.[5] As of Linux kernel version 3.15, released on 8 June 2014, zram supports LZ4 compression algorithm, while LZO remains as the default compression backend. Changes in kernel 3.15 also provide performance improvements, as well as the ability to switch the compression algorithm via sysfs.[6]

Google uses zram in Chrome OS and it is also available as an option for Android 4.4 devices.[7][8] Also, Lubuntu started using zram with version 13.10.[9] As of December 2012, Ubuntu considers to enable zram by default on computers with small amounts of RAM installed.[10]

See also


  1. ^ "Increased performance in Linux with zram (virtual swap compressed in ram)". Web Upd8. 2 October 2011. Retrieved 8 November 2011. 
  2. ^  
  3. ^ "ZRAM Might Finally Be Moved Out Of Linux Staging". 2013-08-14. Retrieved 2014-02-09. 
  4. ^ "zRAM Is Still Hoping For A Promotion". 2013-11-25. Retrieved 2014-02-09. 
  5. ^ "1.2. zram: Memory compression mechanism considered stable". Linux kernel 3.14. 2014-03-30. Retrieved 2014-04-01. 
  6. ^ "1.7. zram: LZ4 compression support, improved performance". Linux kernel 3.15. 2014-06-08. Retrieved 2014-06-15. 
  7. ^ Larabel, Michael (28 March 2013). "Google is Enabling zram for Chrome OS By Default". Chrome Story. Retrieved 29 March 2013. 
  8. ^ Google, Android KitKat | Android Developers
  9. ^ "Next Lubuntu provided with zram enabled! – LinuxVillage (en)". 17 October 2013. Retrieved 10 November 2013. 
  10. ^ Dinsan, Francis (8 December 2012). "Ubuntu Linux Considers Greater Usage of zRAM". Retrieved 30 October 2013. 

External links

  • Compcache, Compressed Caching for Linux
  • Nitin Gupta, Compcache: in-memory compressed swapping, LWN, 26 May 2009
  • Dan Magenheimer, In-kernel memory compression, LWN, 3 April 2013

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