Linux kernel - Revision history

JanCeuleers: /* Interrupts */ explain the abbreviation ISR which is used later in this section

2025-06-27T07:33:06Z

Interrupts: explain the abbreviation ISR which is used later in this section

← Previous revision		Revision as of 07:33, 27 June 2025
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	=== Interrupts ===		=== Interrupts ===

	Although the management of [[interrupt]]s could be seen as a single job, it is divided into two. This split in two is due to the different time constraints and to the synchronization needs of the tasks whose the management is composed of. The first part is made up of an asynchronous [[Interrupt handler\|interrupt service routine]] that in Linux is known as the ''top half'', while the second part is carried out by one of three types of the so-called ''bottom halves'' (''softirq'', ''tasklets,'' and ''work queues'').<ref name="LoveRobert2010" />{{Rp\|pages=133–137}}		Although the management of [[interrupt]]s could be seen as a single job, it is divided into two. This split in two is due to the different time constraints and to the synchronization needs of the tasks whose the management is composed of. The first part is made up of an asynchronous [[Interrupt handler\|interrupt service routine]] (ISR) that in Linux is known as the ''top half'', while the second part is carried out by one of three types of the so-called ''bottom halves'' (''softirq'', ''tasklets,'' and ''work queues'').<ref name="LoveRobert2010" />{{Rp\|pages=133–137}}

	Linux interrupt service routines can be nested. A new IRQ can trap into a high priority ISR that preempts any other lower priority ISR.		Linux interrupt service routines can be nested. A new IRQ can trap into a high priority ISR that preempts any other lower priority ISR.

Michalfiser: /* Memory */ typo

2025-06-10T15:50:18Z

Memory: typo

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	* ''ZONE_DMA'': this zone is suitable for [[Direct memory access \| DMA]].		* ''ZONE_DMA'': this zone is suitable for [[Direct memory access \| DMA]].
	* ''ZONE_NORMAL'': for normal memory operations.		* ''ZONE_NORMAL'': for normal memory operations.
	* ''ZONE_HIGHMEM'': part of physical that is only accessible to kernel ~~uisng~~ temporary mapping.		* ''ZONE_HIGHMEM'': part of physical that is only accessible to kernel using temporary mapping.
	Those zones are most common others exist as the official documentation.<ref name="auto"/>		Those zones are most common others exist as the official documentation.<ref name="auto"/>

Cholodu: removed a teeny grammatical error

2025-06-09T22:00:22Z

removed a teeny grammatical error

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	}}		}}

	The '''Linux kernel''' is a [[Free and open-source software\|free and open source]],<ref name="LoveRobert2010">{{Cite book \|last=Love \|first=Robert \|title=Linux kernel development \|publisher=[[Addison-Wesley]] \|year=2010 \|isbn=978-0-672-32946-3 \|edition=3rd \|location=Upper Saddle River, NJ \|oclc=268788260 \|author-link=Robert Love}}</ref>{{Rp\|page=4}} [[Unix-like]] [[kernel (operating system)\|kernel]] that is used in many [[computer systems]] worldwide. The kernel was created by [[Linus Torvalds]] in 1991 and was soon adopted as the kernel for the [[GNU]] [[operating system]] (OS) which was created to be a [[free software\|free]] replacement for [[Unix]]. Since the late 1990s, it has been included in many [[Linux distributions\|operating system distributions]], many of which are called [[Linux]]. One such Linux kernel operating system is [[Android (operating system)\|Android]] which is used in many mobile and embedded devices.		The '''Linux kernel''' is a [[Free and open-source software\|free and open source]]<ref name="LoveRobert2010">{{Cite book \|last=Love \|first=Robert \|title=Linux kernel development \|publisher=[[Addison-Wesley]] \|year=2010 \|isbn=978-0-672-32946-3 \|edition=3rd \|location=Upper Saddle River, NJ \|oclc=268788260 \|author-link=Robert Love}}</ref>{{Rp\|page=4}} [[Unix-like]] [[kernel (operating system)\|kernel]] that is used in many [[computer systems]] worldwide. The kernel was created by [[Linus Torvalds]] in 1991 and was soon adopted as the kernel for the [[GNU]] [[operating system]] (OS) which was created to be a [[free software\|free]] replacement for [[Unix]]. Since the late 1990s, it has been included in many [[Linux distributions\|operating system distributions]], many of which are called [[Linux]]. One such Linux kernel operating system is [[Android (operating system)\|Android]] which is used in many mobile and embedded devices.

	Most of the kernel code is written in [[C (programming language)\|C]] as supported by the [[GNU compiler collection]] (GCC) which has extensions beyond standard C.<ref name="LoveRobert2010" />{{rp\|page=18}}<ref name="oounl">{{cite web\|title=C Extensions (Using the GNU Compiler Collection (GCC))\|url=https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/C-Extensions.html#C-Extensions\|access-date=13 November 2020\|website=gcc.gnu.org\|archive-date=20 November 2020\|archive-url=https://web.archive.org/web/20201120064908/https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/C-Extensions.html#C-Extensions\|url-status=live}}</ref> The code also contains [[assembly language\|assembly]] code for architecture-specific logic such as optimizing memory use and task execution.<ref name="LoveRobert2010" />{{Rp\|pages=379–380}} The kernel has a [[Modular programming\|modular]] design such that modules can be integrated as [[software component]]s {{endash}} including dynamically loaded. The kernel is [[Monolithic kernel\|monolithic]] in an architectural sense since the entire OS kernel runs in [[kernel space]].		Most of the kernel code is written in [[C (programming language)\|C]] as supported by the [[GNU compiler collection]] (GCC) which has extensions beyond standard C.<ref name="LoveRobert2010" />{{rp\|page=18}}<ref name="oounl">{{cite web\|title=C Extensions (Using the GNU Compiler Collection (GCC))\|url=https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/C-Extensions.html#C-Extensions\|access-date=13 November 2020\|website=gcc.gnu.org\|archive-date=20 November 2020\|archive-url=https://web.archive.org/web/20201120064908/https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/C-Extensions.html#C-Extensions\|url-status=live}}</ref> The code also contains [[assembly language\|assembly]] code for architecture-specific logic such as optimizing memory use and task execution.<ref name="LoveRobert2010" />{{Rp\|pages=379–380}} The kernel has a [[Modular programming\|modular]] design such that modules can be integrated as [[software component]]s {{endash}} including dynamically loaded. The kernel is [[Monolithic kernel\|monolithic]] in an architectural sense since the entire OS kernel runs in [[kernel space]].

Loltyrjustice11: /* Popularity */ Quick little typo fix

2025-06-07T02:28:33Z

Popularity: Quick little typo fix

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	{{Main\|Usage share of operating systems}}		{{Main\|Usage share of operating systems}}

	According to the Stack Overflow's annual Developer Survey of 2019, more than ~~the~~ 53% of all respondents have developed software for [[Linux]] and about 27% for [[Android (operating system)\|Android]],<ref name="MqCDa">{{cite web\|url=https://insights.stackoverflow.com/survey/2019/\|title=Stack Overflow Developer Survey 2019 - most popular technologies\|website=Stack Overflow\|access-date=17 March 2020\|archive-date=8 October 2020\|archive-url=https://web.archive.org/web/20201008033536/https://insights.stackoverflow.com/survey/2019/?utm_source=social-share&utm_medium=social&utm_campaign=dev-survey-2019\|url-status=live}}</ref> although only about 25% develop with Linux-based operating systems.<ref name="sXZWF">{{cite web\|url=https://insights.stackoverflow.com/survey/2019#development-environments-and-tools\|title=Stack Overflow Developer Survey 2019 - development environments and tools\|website=Stack Overflow\|access-date=17 March 2020\|archive-date=7 March 2020\|archive-url=https://web.archive.org/web/20200307082721/https://insights.stackoverflow.com/survey/2019#development-environments-and-tools\|url-status=live}}</ref>		According to the Stack Overflow's annual Developer Survey of 2019, more than 53% of all respondents have developed software for [[Linux]] and about 27% for [[Android (operating system)\|Android]],<ref name="MqCDa">{{cite web\|url=https://insights.stackoverflow.com/survey/2019/\|title=Stack Overflow Developer Survey 2019 - most popular technologies\|website=Stack Overflow\|access-date=17 March 2020\|archive-date=8 October 2020\|archive-url=https://web.archive.org/web/20201008033536/https://insights.stackoverflow.com/survey/2019/?utm_source=social-share&utm_medium=social&utm_campaign=dev-survey-2019\|url-status=live}}</ref> although only about 25% develop with Linux-based operating systems.<ref name="sXZWF">{{cite web\|url=https://insights.stackoverflow.com/survey/2019#development-environments-and-tools\|title=Stack Overflow Developer Survey 2019 - development environments and tools\|website=Stack Overflow\|access-date=17 March 2020\|archive-date=7 March 2020\|archive-url=https://web.archive.org/web/20200307082721/https://insights.stackoverflow.com/survey/2019#development-environments-and-tools\|url-status=live}}</ref>

	Most websites run on [[Linux\|Linux-based operating systems]],<ref name="vjxfE">{{cite web\|title=Usage Statistics and Market Share of Operating Systems for Websites, March 2020\|url=https://w3techs.com/technologies/overview/operating_system\|access-date=17 March 2020\|website=w3techs.com}}</ref><ref name="qUSpE">{{cite web\|title=Usage Statistics and Market Share of Unix for Websites, March 2020\|url=https://w3techs.com/technologies/details/os-unix\|access-date=17 March 2020\|website=w3techs.com}}</ref> and all of the [[TOP500\|world's 500 most powerful supercomputers]] run on Linux.<ref name="top500stats2">{{cite web\|title=TOP500 Supercomputer Sites: Operating system Family / Linux\|url=https://www.top500.org/statistics/details/osfam/1\|access-date=5 October 2019\|publisher=Top500.org\|archive-date=19 November 2012\|archive-url=https://web.archive.org/web/20121119205719/https://www.top500.org/statistics/details/osfam/1\|url-status=live}}</ref>		Most websites run on [[Linux\|Linux-based operating systems]],<ref name="vjxfE">{{cite web\|title=Usage Statistics and Market Share of Operating Systems for Websites, March 2020\|url=https://w3techs.com/technologies/overview/operating_system\|access-date=17 March 2020\|website=w3techs.com}}</ref><ref name="qUSpE">{{cite web\|title=Usage Statistics and Market Share of Unix for Websites, March 2020\|url=https://w3techs.com/technologies/details/os-unix\|access-date=17 March 2020\|website=w3techs.com}}</ref> and all of the [[TOP500\|world's 500 most powerful supercomputers]] run on Linux.<ref name="top500stats2">{{cite web\|title=TOP500 Supercomputer Sites: Operating system Family / Linux\|url=https://www.top500.org/statistics/details/osfam/1\|access-date=5 October 2019\|publisher=Top500.org\|archive-date=19 November 2012\|archive-url=https://web.archive.org/web/20121119205719/https://www.top500.org/statistics/details/osfam/1\|url-status=live}}</ref>

Henkeeee: added space in infobox

2025-05-27T08:56:54Z

added space in infobox

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	\| developer = Community contributors <br /> [[Linus Torvalds]]		\| developer = Community contributors <br /> [[Linus Torvalds]]
	\| programming language = [[C (programming language)\|C]] ([[C11 (C standard revision)\|C11]] since 5.18, [[C89 (C version)\|C89]] before),<ref>{{cite web \|url=https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e8c07082a810f \|title=Kbuild: move to -std=gnu11 \|first=Arnd \|last=Bergmann \|date=3 March 2022 \|website=git.kernel.org}}</ref><br /> [[Assembly language]],<br />		\| programming language = [[C (programming language)\|C]] ([[C11 (C standard revision)\|C11]] since 5.18, [[C89 (C version)\|C89]] before),<ref>{{cite web \|url=https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e8c07082a810f \|title=Kbuild: move to -std=gnu11 \|first=Arnd \|last=Bergmann \|date=3 March 2022 \|website=git.kernel.org}}</ref><br /> [[Assembly language]],<br />
	[[Rust (programming language)\|Rust]],others		[[Rust (programming language)\|Rust]], others
	\| released = 0.02 <small>({{Start date and age\|1991\|10\|5\|df=yes}})</small><!--note that 0.01 was not released to public-->		\| released = 0.02 <small>({{Start date and age\|1991\|10\|5\|df=yes}})</small><!--note that 0.01 was not released to public-->
	\| latest release version = {{wikidata\|property\|preferred\|references\|edit\|Q14579\|P348\|P548=Q2804309}}		\| latest release version = {{wikidata\|property\|preferred\|references\|edit\|Q14579\|P348\|P548=Q2804309}}

D4n2016: /* Popularity */Fixed wording

2025-05-25T14:17:22Z

Popularity: Fixed wording

← Previous revision		Revision as of 14:17, 25 May 2025
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	[[Linux distributions]] bundle the kernel with [[system software]] (e.g., the [[GNU C Library]], [[systemd]], and other [[Unix]] [[Utility software\|utilities]] and [[Daemon (computing)\|daemons]]) and a wide selection of [[application software]], but their [[Usage share of desktop operating systems\|usage share]] in desktops is low in comparison to other operating systems.		[[Linux distributions]] bundle the kernel with [[system software]] (e.g., the [[GNU C Library]], [[systemd]], and other [[Unix]] [[Utility software\|utilities]] and [[Daemon (computing)\|daemons]]) and a wide selection of [[application software]], but their [[Usage share of desktop operating systems\|usage share]] in desktops is low in comparison to other operating systems.

	Since [[Android (operating system)\|Android]], which is Linux, accounts for the majority of mobile device operating systems,<ref name="OVx4S">{{cite press release \|title=Gartner Says Sales of Tablets Will Represent Less Than 10 Percent of All Devices in 2014 \|url=http://www.gartner.com/newsroom/id/2875017 \|location=[[Egham\|Egham, UK]] \|publisher=[[Gartner]] \|date=15 October 2014 \|access-date=19 October 2014 \|archive-date=17 October 2014 \|archive-url=https://web.archive.org/web/20141017151529/http://www.gartner.com/newsroom/id/2875017 \|url-status=dead}}</ref><ref name="oQC5P">{{cite web \|url=https://techcrunch.com/2014/10/15/tablet-sales-growth-plummets-in-2014-as-android-smartphones-continue-to-soar-gartner \|title=Tablet Sales Growth Plummets In 2014 As Android Smartphones Continue To Soar: Gartner \|last=Lunden \|first=Ingrid \|date=15 October 2014 \|work=[[TechCrunch]] \|publisher=[[AOL]] \|access-date=23 October 2014 \|archive-date=23 October 2014 \|archive-url=https://web.archive.org/web/20141023114800/http://techcrunch.com/2014/10/15/tablet-sales-growth-plummets-in-2014-as-android-smartphones-continue-to-soar-gartner/ \|url-status=live}}</ref><ref name="2c2eU">{{cite press release \|title=Global PC Shipments Exceed Forecast with Mild Improvement in Consumer Demand, While Apple Moves to #5 Spot, According to IDC \|url=http://www.idc.com/getdoc.jsp?containerId=prUS25187214 \|location=[[Framingham, Massachusetts\|Framingham, MA]] \|publisher=[[International Data Corporation\|IDC]] \|date=8 October 2014 \|access-date=19 October 2014 \|url-status=dead \|archive-url=https://web.archive.org/web/20141011215307/http://www.idc.com/getdoc.jsp?containerId=prUS25187214 \|archive-date=11 October 2014 }}</ref> and due to its rising use in [[Linux on embedded systems\|embedded devices]], Android is significantly responsible for rising use of Linux overall.<ref name="Fred Hantelmann 2016 16" />		Since [[Android (operating system)\|Android]], which runs on modified Linux kernel, accounts for the majority of mobile device operating systems,<ref name="OVx4S">{{cite press release \|title=Gartner Says Sales of Tablets Will Represent Less Than 10 Percent of All Devices in 2014 \|url=http://www.gartner.com/newsroom/id/2875017 \|location=[[Egham\|Egham, UK]] \|publisher=[[Gartner]] \|date=15 October 2014 \|access-date=19 October 2014 \|archive-date=17 October 2014 \|archive-url=https://web.archive.org/web/20141017151529/http://www.gartner.com/newsroom/id/2875017 \|url-status=dead}}</ref><ref name="oQC5P">{{cite web \|url=https://techcrunch.com/2014/10/15/tablet-sales-growth-plummets-in-2014-as-android-smartphones-continue-to-soar-gartner \|title=Tablet Sales Growth Plummets In 2014 As Android Smartphones Continue To Soar: Gartner \|last=Lunden \|first=Ingrid \|date=15 October 2014 \|work=[[TechCrunch]] \|publisher=[[AOL]] \|access-date=23 October 2014 \|archive-date=23 October 2014 \|archive-url=https://web.archive.org/web/20141023114800/http://techcrunch.com/2014/10/15/tablet-sales-growth-plummets-in-2014-as-android-smartphones-continue-to-soar-gartner/ \|url-status=live}}</ref><ref name="2c2eU">{{cite press release \|title=Global PC Shipments Exceed Forecast with Mild Improvement in Consumer Demand, While Apple Moves to #5 Spot, According to IDC \|url=http://www.idc.com/getdoc.jsp?containerId=prUS25187214 \|location=[[Framingham, Massachusetts\|Framingham, MA]] \|publisher=[[International Data Corporation\|IDC]] \|date=8 October 2014 \|access-date=19 October 2014 \|url-status=dead \|archive-url=https://web.archive.org/web/20141011215307/http://www.idc.com/getdoc.jsp?containerId=prUS25187214 \|archive-date=11 October 2014 }}</ref> and due to its rising use in [[Linux on embedded systems\|embedded devices]], Android is significantly responsible for rising use of Linux overall.<ref name="Fred Hantelmann 2016 16" />

	== Value ==		== Value ==

Alexbee2: /* Scheduling */ Someone who knows more details than me and can find sources needs to talk about EEVDF's replacement of CFS

2025-05-25T01:28:41Z

Scheduling: Someone who knows more details than me and can find sources needs to talk about EEVDF's replacement of CFS

← Previous revision		Revision as of 01:28, 25 May 2025
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	Linux provides both [[preemption (computing)\|user preemption]] as well as full [[kernel preemption]].<ref name="LoveRobert2010" />{{Rp\|pages=62–63}} Preemption reduces [[latency (engineering)\|latency]], increases responsiveness,<ref name="VRxA1">{{cite web\|title=Lowering Latency in Linux: Introducing a Preemptible Kernel {{!}} Linux Journal\|url=https://www.linuxjournal.com/article/5600\|access-date=17 August 2020\|website=Linuxjournal.com\|archive-date=9 August 2020\|archive-url=https://web.archive.org/web/20200809182228/https://www.linuxjournal.com/article/5600\|url-status=live}}</ref> and makes Linux more suitable for desktop and [[real-time computing\|real-time]] applications.		Linux provides both [[preemption (computing)\|user preemption]] as well as full [[kernel preemption]].<ref name="LoveRobert2010" />{{Rp\|pages=62–63}} Preemption reduces [[latency (engineering)\|latency]], increases responsiveness,<ref name="VRxA1">{{cite web\|title=Lowering Latency in Linux: Introducing a Preemptible Kernel {{!}} Linux Journal\|url=https://www.linuxjournal.com/article/5600\|access-date=17 August 2020\|website=Linuxjournal.com\|archive-date=9 August 2020\|archive-url=https://web.archive.org/web/20200809182228/https://www.linuxjournal.com/article/5600\|url-status=live}}</ref> and makes Linux more suitable for desktop and [[real-time computing\|real-time]] applications.

	For normal tasks, by default, the kernel uses the [[Completely Fair Scheduler]] (CFS) class, introduced in version 2.6.23.<ref name=":5">{{cite mailing list\|title=[patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]\|url=https://lwn.net/Articles/230501/\|last=Molnár\|first=Ingo\|author-link=Ingo Molnár\|date=13 April 2007\|mailing-list=[[LKML]]\|access-date=30 March 2020\|archive-date=3 November 2020\|archive-url=https://web.archive.org/web/20201103034312/https://lwn.net/Articles/230501/\|url-status=live}}</ref> The scheduler is defined as a macro in a C header as <code>SCHED_NORMAL</code>. In other POSIX kernels, a similar policy known as <code>SCHED_OTHER</code> allocates CPU timeslices (i.e, it assigns absolute slices of the processor time depending on either predetermined or dynamically computed priority of each process). The Linux CFS does away with absolute timeslices and assigns a fair proportion of CPU time, as a function of parameters like the total number of runnable processes and the time they have already run; this function also takes into account a kind of weight that depends on their relative priorities (nice values).<ref name="LoveRobert2010" />{{Rp\|pages=46–50}}		For normal tasks, by default, the kernel uses the [[Completely Fair Scheduler]] (CFS) class{{Update inline\|date=May 2025\|reason=EEVDF replaced CFS as of Linux 6.6}}, introduced in version 2.6.23.<ref name=":5">{{cite mailing list\|title=[patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]\|url=https://lwn.net/Articles/230501/\|last=Molnár\|first=Ingo\|author-link=Ingo Molnár\|date=13 April 2007\|mailing-list=[[LKML]]\|access-date=30 March 2020\|archive-date=3 November 2020\|archive-url=https://web.archive.org/web/20201103034312/https://lwn.net/Articles/230501/\|url-status=live}}</ref> The scheduler is defined as a macro in a C header as <code>SCHED_NORMAL</code>. In other POSIX kernels, a similar policy known as <code>SCHED_OTHER</code> allocates CPU timeslices (i.e, it assigns absolute slices of the processor time depending on either predetermined or dynamically computed priority of each process). The Linux CFS does away with absolute timeslices and assigns a fair proportion of CPU time, as a function of parameters like the total number of runnable processes and the time they have already run; this function also takes into account a kind of weight that depends on their relative priorities (nice values).<ref name="LoveRobert2010" />{{Rp\|pages=46–50}}

	With user preemption, the kernel scheduler can replace the current process with the execution of a [[context switch]] to a different one that therefore acquires the computing resources for running (CPU, memory, and more). It makes it according to the CFS algorithm (in particular, it uses a variable called {{Mono\|vruntime}} for sorting entities and then chooses the one that has the smaller vruntime, - i.e., the schedulable entity that has had the least share of CPU time), to the active scheduler policy and to the relative priorities.<ref>{{cite web\|title=CFS Scheduler — The Linux Kernel documentation\|url=https://www.kernel.org/doc/html/latest/scheduler/sched-design-CFS.html#\|access-date=1 May 2021\|website=Kernel.org}}</ref> With kernel preemption, the kernel can preempt itself when an interrupt handler returns, when kernel tasks block, and whenever a subsystem explicitly calls the schedule() function.		With user preemption, the kernel scheduler can replace the current process with the execution of a [[context switch]] to a different one that therefore acquires the computing resources for running (CPU, memory, and more). It makes it according to the CFS algorithm (in particular, it uses a variable called {{Mono\|vruntime}} for sorting entities and then chooses the one that has the smaller vruntime, - i.e., the schedulable entity that has had the least share of CPU time), to the active scheduler policy and to the relative priorities.<ref>{{cite web\|title=CFS Scheduler — The Linux Kernel documentation\|url=https://www.kernel.org/doc/html/latest/scheduler/sched-design-CFS.html#\|access-date=1 May 2021\|website=Kernel.org}}</ref> With kernel preemption, the kernel can preempt itself when an interrupt handler returns, when kernel tasks block, and whenever a subsystem explicitly calls the schedule() function.

Chatul: /* Virtual filesystem */ grammar

2025-05-20T15:14:38Z

Virtual filesystem: grammar

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	===Virtual filesystem===		===Virtual filesystem===
	{{See also \| Virtual file system \| Virtual filesystem}}		{{See also \| Virtual file system \| Virtual filesystem}}
	It is the subsystem that implements filesystem and everything related to filesystem. Linux supports a numerous ~~amount of~~ filesystems with different features and functionality. Because of that it was necessary to implement generic filesystem that is independent from underlying filesystem. [[Virtual filesystem]] exposes other linux subsystems or userspace, [[api \| APIs]] that abstract away the different implementation of underlying filesystem. VFS implements system calls like creat,open,read,write and close.		It is the subsystem that implements filesystem and everything related to filesystem. Linux supports numerous filesystems with different features and functionality. Because of that it was necessary to implement a generic filesystem that is independent from underlying filesystem. [[Virtual filesystem]] exposes other linux subsystems or userspace, [[api \| APIs]] that abstract away the different implementation of underlying filesystem. VFS implements system calls like creat,open,read,write and close.
	VFS implements generic super block<ref>{{Cite web\|url=https://docs.oracle.com/cd/E19683-01/806-4073/fsfilesysappx-3/index.html\|title=The Superblock (System Administration Guide: Basic Administration)\|website=docs.oracle.com}}</ref> and [[Inode \| Inode block]] that is independent from the one that the underlying filesystem has.		VFS implements generic super block<ref>{{Cite web\|url=https://docs.oracle.com/cd/E19683-01/806-4073/fsfilesysappx-3/index.html\|title=The Superblock (System Administration Guide: Basic Administration)\|website=docs.oracle.com}}</ref> and [[Inode \| Inode block]] that is independent from the one that the underlying filesystem has.

Ugly Blobfish: /* Virtual filesystem */

2025-05-20T10:34:00Z

Virtual filesystem

← Previous revision		Revision as of 10:34, 20 May 2025
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	===Virtual filesystem===		===Virtual filesystem===
	{{See also \| Virtual file system \| Virtual filesystem}}		{{See also \| Virtual file system \| Virtual filesystem}}
	It is the subsystem that implements filesystem and everything related to filesystem. Linux supports a ~~nomorous~~ amount of filesystems with different features and functionality. Because of that it was necessary to implement generic filesystem that is independent from underlying filesystem. [[Virtual filesystem]] exposes other linux subsystems or userspace, [[api \| APIs]] that abstract away the different implementation of underlying filesystem. VFS implements system calls like creat,open,read,write and close.		It is the subsystem that implements filesystem and everything related to filesystem. Linux supports a numerous amount of filesystems with different features and functionality. Because of that it was necessary to implement generic filesystem that is independent from underlying filesystem. [[Virtual filesystem]] exposes other linux subsystems or userspace, [[api \| APIs]] that abstract away the different implementation of underlying filesystem. VFS implements system calls like creat,open,read,write and close.
	VFS implements generic super block<ref>{{Cite web\|url=https://docs.oracle.com/cd/E19683-01/806-4073/fsfilesysappx-3/index.html\|title=The Superblock (System Administration Guide: Basic Administration)\|website=docs.oracle.com}}</ref> and [[Inode \| Inode block]] that is independent from the one that the underlying filesystem has.		VFS implements generic super block<ref>{{Cite web\|url=https://docs.oracle.com/cd/E19683-01/806-4073/fsfilesysappx-3/index.html\|title=The Superblock (System Administration Guide: Basic Administration)\|website=docs.oracle.com}}</ref> and [[Inode \| Inode block]] that is independent from the one that the underlying filesystem has.

Maxeto0910: /* Developers */no sentence

2025-05-18T14:37:19Z

Developers: no sentence

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	{{stack\|clear=yes\|		{{stack\|clear=yes\|

	[[File:Linux Kernel Sizes Graph.png\|thumb\|upright=1.5\|Graph of the sizes of Linux Kernel versions in millions of lines of code.<ref>{{Cite web \|title=The Linux Kernel Archives \|url=https://www.kernel.org/ \|access-date=28 February 2023 \|website=www.kernel.org}}</ref>]]		[[File:Linux Kernel Sizes Graph.png\|thumb\|upright=1.5\|Graph of the sizes of Linux Kernel versions in millions of lines of code<ref>{{Cite web \|title=The Linux Kernel Archives \|url=https://www.kernel.org/ \|access-date=28 February 2023 \|website=www.kernel.org}}</ref>]]

	<!-- Archived graph source code below. Replaced with rendered image of this data until graphs are replaced with the chart extension.		<!-- Archived graph source code below. Replaced with rendered image of this data until graphs are replaced with the chart extension.

← Previous revision		Revision as of 02:28, 7 June 2025
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	{{Main\|Usage share of operating systems}}		{{Main\|Usage share of operating systems}}

	According to the Stack Overflow's annual Developer Survey of 2019, more than ~~the~~ 53% of all respondents have developed software for [[Linux]] and about 27% for [[Android (operating system)\|Android]],<ref name="MqCDa">{{cite web\|url=https://insights.stackoverflow.com/survey/2019/\|title=Stack Overflow Developer Survey 2019 - most popular technologies\|website=Stack Overflow\|access-date=17 March 2020\|archive-date=8 October 2020\|archive-url=https://web.archive.org/web/20201008033536/https://insights.stackoverflow.com/survey/2019/?utm_source=social-share&utm_medium=social&utm_campaign=dev-survey-2019\|url-status=live}}</ref> although only about 25% develop with Linux-based operating systems.<ref name="sXZWF">{{cite web\|url=https://insights.stackoverflow.com/survey/2019#development-environments-and-tools\|title=Stack Overflow Developer Survey 2019 - development environments and tools\|website=Stack Overflow\|access-date=17 March 2020\|archive-date=7 March 2020\|archive-url=https://web.archive.org/web/20200307082721/https://insights.stackoverflow.com/survey/2019#development-environments-and-tools\|url-status=live}}</ref>		According to the Stack Overflow's annual Developer Survey of 2019, more than 53% of all respondents have developed software for [[Linux]] and about 27% for [[Android (operating system)\|Android]],<ref name="MqCDa">{{cite web\|url=https://insights.stackoverflow.com/survey/2019/\|title=Stack Overflow Developer Survey 2019 - most popular technologies\|website=Stack Overflow\|access-date=17 March 2020\|archive-date=8 October 2020\|archive-url=https://web.archive.org/web/20201008033536/https://insights.stackoverflow.com/survey/2019/?utm_source=social-share&utm_medium=social&utm_campaign=dev-survey-2019\|url-status=live}}</ref> although only about 25% develop with Linux-based operating systems.<ref name="sXZWF">{{cite web\|url=https://insights.stackoverflow.com/survey/2019#development-environments-and-tools\|title=Stack Overflow Developer Survey 2019 - development environments and tools\|website=Stack Overflow\|access-date=17 March 2020\|archive-date=7 March 2020\|archive-url=https://web.archive.org/web/20200307082721/https://insights.stackoverflow.com/survey/2019#development-environments-and-tools\|url-status=live}}</ref>

	Most websites run on [[Linux\|Linux-based operating systems]],<ref name="vjxfE">{{cite web\|title=Usage Statistics and Market Share of Operating Systems for Websites, March 2020\|url=https://w3techs.com/technologies/overview/operating_system\|access-date=17 March 2020\|website=w3techs.com}}</ref><ref name="qUSpE">{{cite web\|title=Usage Statistics and Market Share of Unix for Websites, March 2020\|url=https://w3techs.com/technologies/details/os-unix\|access-date=17 March 2020\|website=w3techs.com}}</ref> and all of the [[TOP500\|world's 500 most powerful supercomputers]] run on Linux.<ref name="top500stats2">{{cite web\|title=TOP500 Supercomputer Sites: Operating system Family / Linux\|url=https://www.top500.org/statistics/details/osfam/1\|access-date=5 October 2019\|publisher=Top500.org\|archive-date=19 November 2012\|archive-url=https://web.archive.org/web/20121119205719/https://www.top500.org/statistics/details/osfam/1\|url-status=live}}</ref>		Most websites run on [[Linux\|Linux-based operating systems]],<ref name="vjxfE">{{cite web\|title=Usage Statistics and Market Share of Operating Systems for Websites, March 2020\|url=https://w3techs.com/technologies/overview/operating_system\|access-date=17 March 2020\|website=w3techs.com}}</ref><ref name="qUSpE">{{cite web\|title=Usage Statistics and Market Share of Unix for Websites, March 2020\|url=https://w3techs.com/technologies/details/os-unix\|access-date=17 March 2020\|website=w3techs.com}}</ref> and all of the [[TOP500\|world's 500 most powerful supercomputers]] run on Linux.<ref name="top500stats2">{{cite web\|title=TOP500 Supercomputer Sites: Operating system Family / Linux\|url=https://www.top500.org/statistics/details/osfam/1\|access-date=5 October 2019\|publisher=Top500.org\|archive-date=19 November 2012\|archive-url=https://web.archive.org/web/20121119205719/https://www.top500.org/statistics/details/osfam/1\|url-status=live}}</ref>

← Previous revision		Revision as of 08:56, 27 May 2025
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	\| developer = Community contributors <br /> [[Linus Torvalds]]		\| developer = Community contributors <br /> [[Linus Torvalds]]
	\| programming language = [[C (programming language)\|C]] ([[C11 (C standard revision)\|C11]] since 5.18, [[C89 (C version)\|C89]] before),<ref>{{cite web \|url=https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e8c07082a810f \|title=Kbuild: move to -std=gnu11 \|first=Arnd \|last=Bergmann \|date=3 March 2022 \|website=git.kernel.org}}</ref><br /> [[Assembly language]],<br />		\| programming language = [[C (programming language)\|C]] ([[C11 (C standard revision)\|C11]] since 5.18, [[C89 (C version)\|C89]] before),<ref>{{cite web \|url=https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e8c07082a810f \|title=Kbuild: move to -std=gnu11 \|first=Arnd \|last=Bergmann \|date=3 March 2022 \|website=git.kernel.org}}</ref><br /> [[Assembly language]],<br />
	[[Rust (programming language)\|Rust]],others		[[Rust (programming language)\|Rust]], others
	\| released = 0.02 <small>({{Start date and age\|1991\|10\|5\|df=yes}})</small><!--note that 0.01 was not released to public-->		\| released = 0.02 <small>({{Start date and age\|1991\|10\|5\|df=yes}})</small><!--note that 0.01 was not released to public-->
	\| latest release version = {{wikidata\|property\|preferred\|references\|edit\|Q14579\|P348\|P548=Q2804309}}		\| latest release version = {{wikidata\|property\|preferred\|references\|edit\|Q14579\|P348\|P548=Q2804309}}

← Previous revision		Revision as of 01:28, 25 May 2025
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	Linux provides both [[preemption (computing)\|user preemption]] as well as full [[kernel preemption]].<ref name="LoveRobert2010" />{{Rp\|pages=62–63}} Preemption reduces [[latency (engineering)\|latency]], increases responsiveness,<ref name="VRxA1">{{cite web\|title=Lowering Latency in Linux: Introducing a Preemptible Kernel {{!}} Linux Journal\|url=https://www.linuxjournal.com/article/5600\|access-date=17 August 2020\|website=Linuxjournal.com\|archive-date=9 August 2020\|archive-url=https://web.archive.org/web/20200809182228/https://www.linuxjournal.com/article/5600\|url-status=live}}</ref> and makes Linux more suitable for desktop and [[real-time computing\|real-time]] applications.		Linux provides both [[preemption (computing)\|user preemption]] as well as full [[kernel preemption]].<ref name="LoveRobert2010" />{{Rp\|pages=62–63}} Preemption reduces [[latency (engineering)\|latency]], increases responsiveness,<ref name="VRxA1">{{cite web\|title=Lowering Latency in Linux: Introducing a Preemptible Kernel {{!}} Linux Journal\|url=https://www.linuxjournal.com/article/5600\|access-date=17 August 2020\|website=Linuxjournal.com\|archive-date=9 August 2020\|archive-url=https://web.archive.org/web/20200809182228/https://www.linuxjournal.com/article/5600\|url-status=live}}</ref> and makes Linux more suitable for desktop and [[real-time computing\|real-time]] applications.

	For normal tasks, by default, the kernel uses the [[Completely Fair Scheduler]] (CFS) class, introduced in version 2.6.23.<ref name=":5">{{cite mailing list\|title=[patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]\|url=https://lwn.net/Articles/230501/\|last=Molnár\|first=Ingo\|author-link=Ingo Molnár\|date=13 April 2007\|mailing-list=[[LKML]]\|access-date=30 March 2020\|archive-date=3 November 2020\|archive-url=https://web.archive.org/web/20201103034312/https://lwn.net/Articles/230501/\|url-status=live}}</ref> The scheduler is defined as a macro in a C header as <code>SCHED_NORMAL</code>. In other POSIX kernels, a similar policy known as <code>SCHED_OTHER</code> allocates CPU timeslices (i.e, it assigns absolute slices of the processor time depending on either predetermined or dynamically computed priority of each process). The Linux CFS does away with absolute timeslices and assigns a fair proportion of CPU time, as a function of parameters like the total number of runnable processes and the time they have already run; this function also takes into account a kind of weight that depends on their relative priorities (nice values).<ref name="LoveRobert2010" />{{Rp\|pages=46–50}}		For normal tasks, by default, the kernel uses the [[Completely Fair Scheduler]] (CFS) class{{Update inline\|date=May 2025\|reason=EEVDF replaced CFS as of Linux 6.6}}, introduced in version 2.6.23.<ref name=":5">{{cite mailing list\|title=[patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]\|url=https://lwn.net/Articles/230501/\|last=Molnár\|first=Ingo\|author-link=Ingo Molnár\|date=13 April 2007\|mailing-list=[[LKML]]\|access-date=30 March 2020\|archive-date=3 November 2020\|archive-url=https://web.archive.org/web/20201103034312/https://lwn.net/Articles/230501/\|url-status=live}}</ref> The scheduler is defined as a macro in a C header as <code>SCHED_NORMAL</code>. In other POSIX kernels, a similar policy known as <code>SCHED_OTHER</code> allocates CPU timeslices (i.e, it assigns absolute slices of the processor time depending on either predetermined or dynamically computed priority of each process). The Linux CFS does away with absolute timeslices and assigns a fair proportion of CPU time, as a function of parameters like the total number of runnable processes and the time they have already run; this function also takes into account a kind of weight that depends on their relative priorities (nice values).<ref name="LoveRobert2010" />{{Rp\|pages=46–50}}

	With user preemption, the kernel scheduler can replace the current process with the execution of a [[context switch]] to a different one that therefore acquires the computing resources for running (CPU, memory, and more). It makes it according to the CFS algorithm (in particular, it uses a variable called {{Mono\|vruntime}} for sorting entities and then chooses the one that has the smaller vruntime, - i.e., the schedulable entity that has had the least share of CPU time), to the active scheduler policy and to the relative priorities.<ref>{{cite web\|title=CFS Scheduler — The Linux Kernel documentation\|url=https://www.kernel.org/doc/html/latest/scheduler/sched-design-CFS.html#\|access-date=1 May 2021\|website=Kernel.org}}</ref> With kernel preemption, the kernel can preempt itself when an interrupt handler returns, when kernel tasks block, and whenever a subsystem explicitly calls the schedule() function.		With user preemption, the kernel scheduler can replace the current process with the execution of a [[context switch]] to a different one that therefore acquires the computing resources for running (CPU, memory, and more). It makes it according to the CFS algorithm (in particular, it uses a variable called {{Mono\|vruntime}} for sorting entities and then chooses the one that has the smaller vruntime, - i.e., the schedulable entity that has had the least share of CPU time), to the active scheduler policy and to the relative priorities.<ref>{{cite web\|title=CFS Scheduler — The Linux Kernel documentation\|url=https://www.kernel.org/doc/html/latest/scheduler/sched-design-CFS.html#\|access-date=1 May 2021\|website=Kernel.org}}</ref> With kernel preemption, the kernel can preempt itself when an interrupt handler returns, when kernel tasks block, and whenever a subsystem explicitly calls the schedule() function.