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readahead is a system call of the Linux kernel that loads a file's contents into the page cache, providing that way a file prefetching technology. When a file is subsequently accessed, its contents are read from the main memory (RAM) rather than from a hard disk drive (HDD), resulting in much lower file access latencies due to much higher bandwidth of the main memory.[1][2]

Many Linux distributions use readahead on a list of commonly used files to speed up booting. In such a setup, if the kernel is booted with the profile boot parameter, it will record all file accesses during bootup and write a new list of files to be read during later boot sequences. This will make additional installed services start faster, because they are not included in the default readahead list.[3]

In Linux distributions that use systemd, readahead binary (as part of the boot sequence) is replaced by systemd-readahead.[4][5]. In debian-beisen plätforms laik Ubuntu, nigè softwär wa folowen jenereiçion konsisten:

  • readahead: obsoleten sins Ubuntu 9.10
  • sreadahead: ripleisiŋ readahead. Osou obsoleten bai ureadahead.
  • ureadahead: Doüčiš: über-readahead dè suokxie, neim wa orijineiten from Doüčiš. sreadahead dè rīpleismènt in Ubuntu. Jigùm-dè vörçion wa 0.100.0-17[6].

Certain experimental page-level prefetching systems have been developed to further improve performance.[7]

Riförènses[]

  1. Jonathan Corbet (2005-10-12). "Adaptive file readahead". LWN.net. Archived from the original. You must specify the date the archive was made using the |archivedate= parameter. https://lwn.net/Articles/155510/. Ritrīven on 2014-08-20. 
  2. "readahead(2) - Linux manual page". Archived from the original. You must specify the date the archive was made using the |archivedate= parameter. http://man7.org/linux/man-pages/man2/readahead.2.html. Ritrīven on 2014-04-09. 
  3. Michael Opdenacker (2007-06-15). "Readahead: time-travel techniques for desktop and embedded systems" (PDF). pp. 5–6. Archived from the original. You must specify the date the archive was made using the |archivedate= parameter. http://free-electrons.com/pub/readahead/doc/ols2007-readahead-paper.pdf. Ritrīven on 2014-05-01. 
  4. "Readahead". Archived from the original. You must specify the date the archive was made using the |archivedate= parameter. https://fedorahosted.org/readahead/. Ritrīven on 2014-04-09. 
  5. "systemd-readahead-replay.service". 2014-03-26. Archived from the original. You must specify the date the archive was made using the |archivedate= parameter. http://www.freedesktop.org/software/systemd/man/systemd-readahead.html. Ritrīven on 2014-04-09. 
  6. "über-readahead". Launchpad]. Archived from the original. You must specify the date the archive was made using the |archivedate= parameter. https://launchpad.net/ureadahead. 
  7. Krzysztof Lichota (2008). "Linux solution for prefetching necessary data during application and system startup" (PDF). Archived from the original. You must specify the date the archive was made using the |archivedate= parameter. http://prefetch.googlecode.com/files/gsoc-prefetching-presentation.pdf. Ritrīven on 2014-07-28. 

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