This article is about the Linux kernel feature. For the memory hardware technology, see Z-RAM. For the Linux kernel compressed swap cache, see zswap.
zram, formerly called compcache, is a Linux kernel module for creating a compressed block device in RAM, i.e. a RAM disk with on-the-fly disk compression. The block device created with zram can then be used for swap or as general-purpose RAM disk. The two most common uses for zram are for the storage of temporary files (/tmp) and as a swap device. Initially, zram had only the latter function, hence the original name "compcache" ("compressed cache"). Unlike swap, zram only uses 0.1% of the maximum size of the disk when not in use.[1]
zram
Initial release
March 30, 2014; 10 years ago (2014-03-30) (Linux 3.14)
After four years in the Linux kernel's driver staging area, zram was introduced into the mainline Linux kernel in version 3.14, released on March 30, 2014.[2] From Linux kernel version 3.15 onwards (released on June 8, 2014), zram supports multiple compression streams and multiple compression algorithms. Compression algorithms include DEFLATE (DEFLATE), LZ4 (LZ4, and LZ4HC "high compression"), LZO (LZO-RLE "run-length encoding"),[3]Zstandard (ZSTD), 842 (842). From kernel 5.1, the default is LZO-RLE,[3] which has a balance of speed and compression ratio. Like most other system parameters, the compression algorithm can be selected via sysfs.[4]
When used as a compressed swap space, zram is similar to zswap, which is not a general-purpose RAM disk, but rather an in-kernel compressed cache for swap pages. Until the introduction of CONFIG_ZRAM_WRITEBACK in kernel version 4.14, unlike zswap, zram was unable to use a storage device as a backing store, so it was unable to move less-frequently used pages to disk. However, zswap always requires a backing store, which is not the case for zram.
When used for swap, zram (like zswap) allows Linux to make more efficient use of RAM, since the operating system can then hold more pages of memory in the compressed swap than if the same amount of RAM had been used as application memory or disk cache. This is particularly effective on machines that do not have much memory.[5][6] In 2012, Ubuntu briefly considered enabling zram by default on computers with small amounts of installed RAM.[7] For this same reason, Fedora enabled zram by default starting with release 33.[8]
Using compressed swap space with zram or zswap also offers advantages for low-end hardware devices such as embedded devices and netbooks. Such devices usually use flash-based storage, which has limited lifespan due to write amplification, and may also use it to provide swap space. Using zram or zswap reduces the swap usage, which effectively reduces the amount of wear placed on flash-based storage and makes it last longer. Using zram also results in significantly reduced I/O for Linux systems that require swapping.[9][10]
^"zram: Compressed RAM-based block devices — The Linux Kernel documentation". docs.kernel.org. Retrieved February 25, 2024.
^"Linux kernel 3.14, Section 1.2. zram: Memory compression mechanism considered stable". kernelnewbies.org. March 30, 2014. Retrieved April 1, 2014.
^ ab"ZRAM Will See Greater Performance On Linux 5.1 - It Changed Its Default Compressor - Phoronix". www.phoronix.com.
^"Linux kernel 3.15, Section 1.7. zram: LZ4 compression support, improved performance". kernelnewbies.org. June 8, 2014. Retrieved June 15, 2014.
^"Increased performance in Linux with zram (virtual swap compressed in ram)". webupd8.org. October 2, 2011. Retrieved November 8, 2011.
^"compcache Compressed Caching for Linux". code.google.com. April 27, 2010. Retrieved November 11, 2011.
^Dinsan, Francis (December 8, 2012). "Ubuntu Linux Considers Greater Usage of zRAM". Retrieved October 30, 2013.
^"Fedora 33 Looking To Use Swap On zRAM By Default With systemd's zram-generator - Phoronix". www.phoronix.com. Retrieved March 29, 2021.
^"ZRAM Might Finally Be Moved Out Of Linux Staging". Phoronix. August 14, 2013. Retrieved February 9, 2014.
^"zRAM Is Still Hoping For A Promotion". Phoronix. November 25, 2013. Retrieved February 9, 2014.
External linksedit
zram Linux kernel documentation and zramctl(8) manual page
Compcache, Compressed Caching for Linux
Compcache: in-memory compressed swapping, May 26, 2009, LWN.net, by Nitin Gupta
In-kernel memory compression, April 3, 2013, LWN.net, by Dan Magenheimer
The Compression Cache: Virtual Memory Compression for Handheld Computers, March 16, 2000, by Michael J. Freedman
January 01, 1970
zram, this, article, about, linux, kernel, feature, memory, hardware, technology, linux, kernel, compressed, swap, cache, zswap, formerly, called, compcache, linux, kernel, module, creating, compressed, block, device, disk, with, disk, compression, block, devi. This article is about the Linux kernel feature For the memory hardware technology see Z RAM For the Linux kernel compressed swap cache see zswap zram formerly called compcache is a Linux kernel module for creating a compressed block device in RAM i e a RAM disk with on the fly disk compression The block device created with zram can then be used for swap or as general purpose RAM disk The two most common uses for zram are for the storage of temporary files tmp and as a swap device Initially zram had only the latter function hence the original name compcache compressed cache Unlike swap zram only uses 0 1 of the maximum size of the disk when not in use 1 zramInitial releaseMarch 30 2014 10 years ago 2014 03 30 Linux 3 14 Written inCOperating systemLinuxTypeLinux kernel featuresLicenseGNU General Public LicenseWebsitewww wbr kernel wbr org After four years in the Linux kernel s driver staging area zram was introduced into the mainline Linux kernel in version 3 14 released on March 30 2014 2 From Linux kernel version 3 15 onwards released on June 8 2014 zram supports multiple compression streams and multiple compression algorithms Compression algorithms include DEFLATE DEFLATE LZ4 LZ4 and LZ4HC high compression LZO LZO RLE run length encoding 3 Zstandard ZSTD 842 842 From kernel 5 1 the default is LZO RLE 3 which has a balance of speed and compression ratio Like most other system parameters the compression algorithm can be selected via sysfs 4 When used as a compressed swap space zram is similar to zswap which is not a general purpose RAM disk but rather an in kernel compressed cache for swap pages Until the introduction of CONFIG ZRAM WRITEBACK in kernel version 4 14 unlike zswap zram was unable to use a storage device as a backing store so it was unable to move less frequently used pages to disk However zswap always requires a backing store which is not the case for zram When used for swap zram like zswap allows Linux to make more efficient use of RAM since the operating system can then hold more pages of memory in the compressed swap than if the same amount of RAM had been used as application memory or disk cache This is particularly effective on machines that do not have much memory 5 6 In 2012 Ubuntu briefly considered enabling zram by default on computers with small amounts of installed RAM 7 For this same reason Fedora enabled zram by default starting with release 33 8 Using compressed swap space with zram or zswap also offers advantages for low end hardware devices such as embedded devices and netbooks Such devices usually use flash based storage which has limited lifespan due to write amplification and may also use it to provide swap space Using zram or zswap reduces the swap usage which effectively reduces the amount of wear placed on flash based storage and makes it last longer Using zram also results in significantly reduced I O for Linux systems that require swapping 9 10 See also edit nbsp Linux portal Swap partitions on SSDs Virtual memory compressionReferences edit zram Compressed RAM based block devices The Linux Kernel documentation docs kernel org Retrieved February 25 2024 Linux kernel 3 14 Section 1 2 zram Memory compression mechanism considered stable kernelnewbies org March 30 2014 Retrieved April 1 2014 a b ZRAM Will See Greater Performance On Linux 5 1 It Changed Its Default Compressor Phoronix www phoronix com Linux kernel 3 15 Section 1 7 zram LZ4 compression support improved performance kernelnewbies org June 8 2014 Retrieved June 15 2014 Increased performance in Linux with zram virtual swap compressed in ram webupd8 org October 2 2011 Retrieved November 8 2011 compcache Compressed Caching for Linux code google com April 27 2010 Retrieved November 11 2011 Dinsan Francis December 8 2012 Ubuntu Linux Considers Greater Usage of zRAM Retrieved October 30 2013 Fedora 33 Looking To Use Swap On zRAM By Default With systemd s zram generator Phoronix www phoronix com Retrieved March 29 2021 ZRAM Might Finally Be Moved Out Of Linux Staging Phoronix August 14 2013 Retrieved February 9 2014 zRAM Is Still Hoping For A Promotion Phoronix November 25 2013 Retrieved February 9 2014 External links editzram Linux kernel documentation and zramctl 8 manual page Compcache Compressed Caching for Linux Compcache in memory compressed swapping May 26 2009 LWN net by Nitin Gupta In kernel memory compression April 3 2013 LWN net by Dan Magenheimer The Compression Cache Virtual Memory Compression for Handheld Computers March 16 2000 by Michael J Freedman Retrieved from https en wikipedia org w index php title Zram amp oldid 1214095931, wikipedia, wiki, book, books, library,
