1 # SPDX-License-Identifier: GPL-2.0-only
6 default "/lib/modules/$(shell,uname -r)/.config"
7 default "/etc/kernel-config"
8 default "/boot/config-$(shell,uname -r)"
10 default "arch/$(ARCH)/defconfig"
13 def_bool $(success,$(CC) --version | head -n 1 | grep -q gcc)
17 default $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) if CC_IS_GCC
21 def_bool $(success,$(CC) --version | head -n 1 | grep -q clang)
25 default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
28 def_bool $(success,$(srctree)/scripts/cc-can-link.sh $(CC))
30 config CC_HAS_ASM_GOTO
31 def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
33 config TOOLS_SUPPORT_RELR
34 def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
36 config CC_HAS_ASM_INLINE
37 def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
39 config CC_HAS_WARN_MAYBE_UNINITIALIZED
40 def_bool $(cc-option,-Wmaybe-uninitialized)
42 GCC >= 4.7 supports this option.
44 config CC_DISABLE_WARN_MAYBE_UNINITIALIZED
46 depends on CC_HAS_WARN_MAYBE_UNINITIALIZED
47 default CC_IS_GCC && GCC_VERSION < 40900 # unreliable for GCC < 4.9
49 GCC's -Wmaybe-uninitialized is not reliable by definition.
50 Lots of false positive warnings are produced in some cases.
52 If this option is enabled, -Wno-maybe-uninitialzed is passed
53 to the compiler to suppress maybe-uninitialized warnings.
61 config BUILDTIME_EXTABLE_SORT
64 config THREAD_INFO_IN_TASK
67 Select this to move thread_info off the stack into task_struct. To
68 make this work, an arch will need to remove all thread_info fields
69 except flags and fix any runtime bugs.
71 One subtle change that will be needed is to use try_get_task_stack()
72 and put_task_stack() in save_thread_stack_tsk() and get_wchan().
81 depends on BROKEN || !SMP
84 config INIT_ENV_ARG_LIMIT
89 Maximum of each of the number of arguments and environment
90 variables passed to init from the kernel command line.
93 bool "Compile also drivers which will not load"
97 Some drivers can be compiled on a different platform than they are
98 intended to be run on. Despite they cannot be loaded there (or even
99 when they load they cannot be used due to missing HW support),
100 developers still, opposing to distributors, might want to build such
101 drivers to compile-test them.
103 If you are a developer and want to build everything available, say Y
104 here. If you are a user/distributor, say N here to exclude useless
105 drivers to be distributed.
107 config UAPI_HEADER_TEST
108 bool "Compile test UAPI headers"
109 depends on HEADERS_INSTALL && CC_CAN_LINK
111 Compile test headers exported to user-space to ensure they are
112 self-contained, i.e. compilable as standalone units.
114 If you are a developer or tester and want to ensure the exported
115 headers are self-contained, say Y here. Otherwise, choose N.
118 string "Local version - append to kernel release"
120 Append an extra string to the end of your kernel version.
121 This will show up when you type uname, for example.
122 The string you set here will be appended after the contents of
123 any files with a filename matching localversion* in your
124 object and source tree, in that order. Your total string can
125 be a maximum of 64 characters.
127 config LOCALVERSION_AUTO
128 bool "Automatically append version information to the version string"
130 depends on !COMPILE_TEST
132 This will try to automatically determine if the current tree is a
133 release tree by looking for git tags that belong to the current
134 top of tree revision.
136 A string of the format -gxxxxxxxx will be added to the localversion
137 if a git-based tree is found. The string generated by this will be
138 appended after any matching localversion* files, and after the value
139 set in CONFIG_LOCALVERSION.
141 (The actual string used here is the first eight characters produced
142 by running the command:
144 $ git rev-parse --verify HEAD
146 which is done within the script "scripts/setlocalversion".)
149 string "Build ID Salt"
152 The build ID is used to link binaries and their debug info. Setting
153 this option will use the value in the calculation of the build id.
154 This is mostly useful for distributions which want to ensure the
155 build is unique between builds. It's safe to leave the default.
157 config HAVE_KERNEL_GZIP
160 config HAVE_KERNEL_BZIP2
163 config HAVE_KERNEL_LZMA
166 config HAVE_KERNEL_XZ
169 config HAVE_KERNEL_LZO
172 config HAVE_KERNEL_LZ4
175 config HAVE_KERNEL_UNCOMPRESSED
179 prompt "Kernel compression mode"
181 depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_UNCOMPRESSED
183 The linux kernel is a kind of self-extracting executable.
184 Several compression algorithms are available, which differ
185 in efficiency, compression and decompression speed.
186 Compression speed is only relevant when building a kernel.
187 Decompression speed is relevant at each boot.
189 If you have any problems with bzip2 or lzma compressed
190 kernels, mail me (Alain Knaff) <alain@knaff.lu>. (An older
191 version of this functionality (bzip2 only), for 2.4, was
192 supplied by Christian Ludwig)
194 High compression options are mostly useful for users, who
195 are low on disk space (embedded systems), but for whom ram
198 If in doubt, select 'gzip'
202 depends on HAVE_KERNEL_GZIP
204 The old and tried gzip compression. It provides a good balance
205 between compression ratio and decompression speed.
209 depends on HAVE_KERNEL_BZIP2
211 Its compression ratio and speed is intermediate.
212 Decompression speed is slowest among the choices. The kernel
213 size is about 10% smaller with bzip2, in comparison to gzip.
214 Bzip2 uses a large amount of memory. For modern kernels you
215 will need at least 8MB RAM or more for booting.
219 depends on HAVE_KERNEL_LZMA
221 This compression algorithm's ratio is best. Decompression speed
222 is between gzip and bzip2. Compression is slowest.
223 The kernel size is about 33% smaller with LZMA in comparison to gzip.
227 depends on HAVE_KERNEL_XZ
229 XZ uses the LZMA2 algorithm and instruction set specific
230 BCJ filters which can improve compression ratio of executable
231 code. The size of the kernel is about 30% smaller with XZ in
232 comparison to gzip. On architectures for which there is a BCJ
233 filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
234 will create a few percent smaller kernel than plain LZMA.
236 The speed is about the same as with LZMA: The decompression
237 speed of XZ is better than that of bzip2 but worse than gzip
238 and LZO. Compression is slow.
242 depends on HAVE_KERNEL_LZO
244 Its compression ratio is the poorest among the choices. The kernel
245 size is about 10% bigger than gzip; however its speed
246 (both compression and decompression) is the fastest.
250 depends on HAVE_KERNEL_LZ4
252 LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
253 A preliminary version of LZ4 de/compression tool is available at
254 <https://code.google.com/p/lz4/>.
256 Its compression ratio is worse than LZO. The size of the kernel
257 is about 8% bigger than LZO. But the decompression speed is
260 config KERNEL_UNCOMPRESSED
262 depends on HAVE_KERNEL_UNCOMPRESSED
264 Produce uncompressed kernel image. This option is usually not what
265 you want. It is useful for debugging the kernel in slow simulation
266 environments, where decompressing and moving the kernel is awfully
267 slow. This option allows early boot code to skip the decompressor
268 and jump right at uncompressed kernel image.
272 config DEFAULT_HOSTNAME
273 string "Default hostname"
276 This option determines the default system hostname before userspace
277 calls sethostname(2). The kernel traditionally uses "(none)" here,
278 but you may wish to use a different default here to make a minimal
279 system more usable with less configuration.
282 # For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can
283 # add proper SWAP support to them, in which case this can be remove.
289 bool "Support for paging of anonymous memory (swap)"
290 depends on MMU && BLOCK && !ARCH_NO_SWAP
293 This option allows you to choose whether you want to have support
294 for so called swap devices or swap files in your kernel that are
295 used to provide more virtual memory than the actual RAM present
296 in your computer. If unsure say Y.
301 Inter Process Communication is a suite of library functions and
302 system calls which let processes (running programs) synchronize and
303 exchange information. It is generally considered to be a good thing,
304 and some programs won't run unless you say Y here. In particular, if
305 you want to run the DOS emulator dosemu under Linux (read the
306 DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
307 you'll need to say Y here.
309 You can find documentation about IPC with "info ipc" and also in
310 section 6.4 of the Linux Programmer's Guide, available from
311 <http://www.tldp.org/guides.html>.
313 config SYSVIPC_SYSCTL
320 bool "POSIX Message Queues"
323 POSIX variant of message queues is a part of IPC. In POSIX message
324 queues every message has a priority which decides about succession
325 of receiving it by a process. If you want to compile and run
326 programs written e.g. for Solaris with use of its POSIX message
327 queues (functions mq_*) say Y here.
329 POSIX message queues are visible as a filesystem called 'mqueue'
330 and can be mounted somewhere if you want to do filesystem
331 operations on message queues.
335 config POSIX_MQUEUE_SYSCTL
337 depends on POSIX_MQUEUE
341 config CROSS_MEMORY_ATTACH
342 bool "Enable process_vm_readv/writev syscalls"
346 Enabling this option adds the system calls process_vm_readv and
347 process_vm_writev which allow a process with the correct privileges
348 to directly read from or write to another process' address space.
349 See the man page for more details.
352 bool "uselib syscall"
353 def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
355 This option enables the uselib syscall, a system call used in the
356 dynamic linker from libc5 and earlier. glibc does not use this
357 system call. If you intend to run programs built on libc5 or
358 earlier, you may need to enable this syscall. Current systems
359 running glibc can safely disable this.
362 bool "Auditing support"
365 Enable auditing infrastructure that can be used with another
366 kernel subsystem, such as SELinux (which requires this for
367 logging of avc messages output). System call auditing is included
368 on architectures which support it.
370 config HAVE_ARCH_AUDITSYSCALL
375 depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
378 source "kernel/irq/Kconfig"
379 source "kernel/time/Kconfig"
380 source "kernel/Kconfig.preempt"
382 menu "CPU/Task time and stats accounting"
384 config VIRT_CPU_ACCOUNTING
388 prompt "Cputime accounting"
389 default TICK_CPU_ACCOUNTING if !PPC64
390 default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
392 # Kind of a stub config for the pure tick based cputime accounting
393 config TICK_CPU_ACCOUNTING
394 bool "Simple tick based cputime accounting"
395 depends on !S390 && !NO_HZ_FULL
397 This is the basic tick based cputime accounting that maintains
398 statistics about user, system and idle time spent on per jiffies
403 config VIRT_CPU_ACCOUNTING_NATIVE
404 bool "Deterministic task and CPU time accounting"
405 depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
406 select VIRT_CPU_ACCOUNTING
408 Select this option to enable more accurate task and CPU time
409 accounting. This is done by reading a CPU counter on each
410 kernel entry and exit and on transitions within the kernel
411 between system, softirq and hardirq state, so there is a
412 small performance impact. In the case of s390 or IBM POWER > 5,
413 this also enables accounting of stolen time on logically-partitioned
416 config VIRT_CPU_ACCOUNTING_GEN
417 bool "Full dynticks CPU time accounting"
418 depends on HAVE_CONTEXT_TRACKING
419 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
420 depends on GENERIC_CLOCKEVENTS
421 select VIRT_CPU_ACCOUNTING
422 select CONTEXT_TRACKING
424 Select this option to enable task and CPU time accounting on full
425 dynticks systems. This accounting is implemented by watching every
426 kernel-user boundaries using the context tracking subsystem.
427 The accounting is thus performed at the expense of some significant
430 For now this is only useful if you are working on the full
431 dynticks subsystem development.
437 config IRQ_TIME_ACCOUNTING
438 bool "Fine granularity task level IRQ time accounting"
439 depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
441 Select this option to enable fine granularity task irq time
442 accounting. This is done by reading a timestamp on each
443 transitions between softirq and hardirq state, so there can be a
444 small performance impact.
446 If in doubt, say N here.
448 config HAVE_SCHED_AVG_IRQ
450 depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
453 config BSD_PROCESS_ACCT
454 bool "BSD Process Accounting"
457 If you say Y here, a user level program will be able to instruct the
458 kernel (via a special system call) to write process accounting
459 information to a file: whenever a process exits, information about
460 that process will be appended to the file by the kernel. The
461 information includes things such as creation time, owning user,
462 command name, memory usage, controlling terminal etc. (the complete
463 list is in the struct acct in <file:include/linux/acct.h>). It is
464 up to the user level program to do useful things with this
465 information. This is generally a good idea, so say Y.
467 config BSD_PROCESS_ACCT_V3
468 bool "BSD Process Accounting version 3 file format"
469 depends on BSD_PROCESS_ACCT
472 If you say Y here, the process accounting information is written
473 in a new file format that also logs the process IDs of each
474 process and its parent. Note that this file format is incompatible
475 with previous v0/v1/v2 file formats, so you will need updated tools
476 for processing it. A preliminary version of these tools is available
477 at <http://www.gnu.org/software/acct/>.
480 bool "Export task/process statistics through netlink"
485 Export selected statistics for tasks/processes through the
486 generic netlink interface. Unlike BSD process accounting, the
487 statistics are available during the lifetime of tasks/processes as
488 responses to commands. Like BSD accounting, they are sent to user
493 config TASK_DELAY_ACCT
494 bool "Enable per-task delay accounting"
498 Collect information on time spent by a task waiting for system
499 resources like cpu, synchronous block I/O completion and swapping
500 in pages. Such statistics can help in setting a task's priorities
501 relative to other tasks for cpu, io, rss limits etc.
506 bool "Enable extended accounting over taskstats"
509 Collect extended task accounting data and send the data
510 to userland for processing over the taskstats interface.
514 config TASK_IO_ACCOUNTING
515 bool "Enable per-task storage I/O accounting"
516 depends on TASK_XACCT
518 Collect information on the number of bytes of storage I/O which this
524 bool "Pressure stall information tracking"
526 Collect metrics that indicate how overcommitted the CPU, memory,
527 and IO capacity are in the system.
529 If you say Y here, the kernel will create /proc/pressure/ with the
530 pressure statistics files cpu, memory, and io. These will indicate
531 the share of walltime in which some or all tasks in the system are
532 delayed due to contention of the respective resource.
534 In kernels with cgroup support, cgroups (cgroup2 only) will
535 have cpu.pressure, memory.pressure, and io.pressure files,
536 which aggregate pressure stalls for the grouped tasks only.
538 For more details see Documentation/accounting/psi.rst.
542 config PSI_DEFAULT_DISABLED
543 bool "Require boot parameter to enable pressure stall information tracking"
547 If set, pressure stall information tracking will be disabled
548 per default but can be enabled through passing psi=1 on the
549 kernel commandline during boot.
551 This feature adds some code to the task wakeup and sleep
552 paths of the scheduler. The overhead is too low to affect
553 common scheduling-intense workloads in practice (such as
554 webservers, memcache), but it does show up in artificial
555 scheduler stress tests, such as hackbench.
557 If you are paranoid and not sure what the kernel will be
562 endmenu # "CPU/Task time and stats accounting"
566 depends on SMP || COMPILE_TEST
569 Make sure that CPUs running critical tasks are not disturbed by
570 any source of "noise" such as unbound workqueues, timers, kthreads...
571 Unbound jobs get offloaded to housekeeping CPUs. This is driven by
572 the "isolcpus=" boot parameter.
576 source "kernel/rcu/Kconfig"
583 tristate "Kernel .config support"
585 This option enables the complete Linux kernel ".config" file
586 contents to be saved in the kernel. It provides documentation
587 of which kernel options are used in a running kernel or in an
588 on-disk kernel. This information can be extracted from the kernel
589 image file with the script scripts/extract-ikconfig and used as
590 input to rebuild the current kernel or to build another kernel.
591 It can also be extracted from a running kernel by reading
592 /proc/config.gz if enabled (below).
595 bool "Enable access to .config through /proc/config.gz"
596 depends on IKCONFIG && PROC_FS
598 This option enables access to the kernel configuration file
599 through /proc/config.gz.
602 tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
605 This option enables access to the in-kernel headers that are generated during
606 the build process. These can be used to build eBPF tracing programs,
607 or similar programs. If you build the headers as a module, a module called
608 kheaders.ko is built which can be loaded on-demand to get access to headers.
611 int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
616 Select the minimal kernel log buffer size as a power of 2.
617 The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
618 parameter, see below. Any higher size also might be forced
619 by "log_buf_len" boot parameter.
629 config LOG_CPU_MAX_BUF_SHIFT
630 int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
633 default 12 if !BASE_SMALL
634 default 0 if BASE_SMALL
637 This option allows to increase the default ring buffer size
638 according to the number of CPUs. The value defines the contribution
639 of each CPU as a power of 2. The used space is typically only few
640 lines however it might be much more when problems are reported,
643 The increased size means that a new buffer has to be allocated and
644 the original static one is unused. It makes sense only on systems
645 with more CPUs. Therefore this value is used only when the sum of
646 contributions is greater than the half of the default kernel ring
647 buffer as defined by LOG_BUF_SHIFT. The default values are set
648 so that more than 64 CPUs are needed to trigger the allocation.
650 Also this option is ignored when "log_buf_len" kernel parameter is
651 used as it forces an exact (power of two) size of the ring buffer.
653 The number of possible CPUs is used for this computation ignoring
654 hotplugging making the computation optimal for the worst case
655 scenario while allowing a simple algorithm to be used from bootup.
657 Examples shift values and their meaning:
658 17 => 128 KB for each CPU
659 16 => 64 KB for each CPU
660 15 => 32 KB for each CPU
661 14 => 16 KB for each CPU
662 13 => 8 KB for each CPU
663 12 => 4 KB for each CPU
665 config PRINTK_SAFE_LOG_BUF_SHIFT
666 int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
671 Select the size of an alternate printk per-CPU buffer where messages
672 printed from usafe contexts are temporary stored. One example would
673 be NMI messages, another one - printk recursion. The messages are
674 copied to the main log buffer in a safe context to avoid a deadlock.
675 The value defines the size as a power of 2.
677 Those messages are rare and limited. The largest one is when
678 a backtrace is printed. It usually fits into 4KB. Select
679 8KB if you want to be on the safe side.
682 17 => 128 KB for each CPU
683 16 => 64 KB for each CPU
684 15 => 32 KB for each CPU
685 14 => 16 KB for each CPU
686 13 => 8 KB for each CPU
687 12 => 4 KB for each CPU
690 # Architectures with an unreliable sched_clock() should select this:
692 config HAVE_UNSTABLE_SCHED_CLOCK
695 config GENERIC_SCHED_CLOCK
698 menu "Scheduler features"
701 bool "Enable utilization clamping for RT/FAIR tasks"
702 depends on CPU_FREQ_GOV_SCHEDUTIL
704 This feature enables the scheduler to track the clamped utilization
705 of each CPU based on RUNNABLE tasks scheduled on that CPU.
707 With this option, the user can specify the min and max CPU
708 utilization allowed for RUNNABLE tasks. The max utilization defines
709 the maximum frequency a task should use while the min utilization
710 defines the minimum frequency it should use.
712 Both min and max utilization clamp values are hints to the scheduler,
713 aiming at improving its frequency selection policy, but they do not
714 enforce or grant any specific bandwidth for tasks.
718 config UCLAMP_BUCKETS_COUNT
719 int "Number of supported utilization clamp buckets"
722 depends on UCLAMP_TASK
724 Defines the number of clamp buckets to use. The range of each bucket
725 will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the
726 number of clamp buckets the finer their granularity and the higher
727 the precision of clamping aggregation and tracking at run-time.
729 For example, with the minimum configuration value we will have 5
730 clamp buckets tracking 20% utilization each. A 25% boosted tasks will
731 be refcounted in the [20..39]% bucket and will set the bucket clamp
732 effective value to 25%.
733 If a second 30% boosted task should be co-scheduled on the same CPU,
734 that task will be refcounted in the same bucket of the first task and
735 it will boost the bucket clamp effective value to 30%.
736 The clamp effective value of a bucket is reset to its nominal value
737 (20% in the example above) when there are no more tasks refcounted in
740 An additional boost/capping margin can be added to some tasks. In the
741 example above the 25% task will be boosted to 30% until it exits the
742 CPU. If that should be considered not acceptable on certain systems,
743 it's always possible to reduce the margin by increasing the number of
744 clamp buckets to trade off used memory for run-time tracking
747 If in doubt, use the default value.
752 # For architectures that want to enable the support for NUMA-affine scheduler
755 config ARCH_SUPPORTS_NUMA_BALANCING
759 # For architectures that prefer to flush all TLBs after a number of pages
760 # are unmapped instead of sending one IPI per page to flush. The architecture
761 # must provide guarantees on what happens if a clean TLB cache entry is
762 # written after the unmap. Details are in mm/rmap.c near the check for
763 # should_defer_flush. The architecture should also consider if the full flush
764 # and the refill costs are offset by the savings of sending fewer IPIs.
765 config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
770 depends on !$(cc-option,-D__SIZEOF_INT128__=0)
773 # For architectures that know their GCC __int128 support is sound
775 config ARCH_SUPPORTS_INT128
778 # For architectures that (ab)use NUMA to represent different memory regions
779 # all cpu-local but of different latencies, such as SuperH.
781 config ARCH_WANT_NUMA_VARIABLE_LOCALITY
784 config NUMA_BALANCING
785 bool "Memory placement aware NUMA scheduler"
786 depends on ARCH_SUPPORTS_NUMA_BALANCING
787 depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
788 depends on SMP && NUMA && MIGRATION
790 This option adds support for automatic NUMA aware memory/task placement.
791 The mechanism is quite primitive and is based on migrating memory when
792 it has references to the node the task is running on.
794 This system will be inactive on UMA systems.
796 config NUMA_BALANCING_DEFAULT_ENABLED
797 bool "Automatically enable NUMA aware memory/task placement"
799 depends on NUMA_BALANCING
801 If set, automatic NUMA balancing will be enabled if running on a NUMA
805 bool "Control Group support"
808 This option adds support for grouping sets of processes together, for
809 use with process control subsystems such as Cpusets, CFS, memory
810 controls or device isolation.
812 - Documentation/scheduler/sched-design-CFS.rst (CFS)
813 - Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation
814 and resource control)
824 bool "Memory controller"
828 Provides control over the memory footprint of tasks in a cgroup.
831 bool "Swap controller"
832 depends on MEMCG && SWAP
834 Provides control over the swap space consumed by tasks in a cgroup.
836 config MEMCG_SWAP_ENABLED
837 bool "Swap controller enabled by default"
838 depends on MEMCG_SWAP
841 Memory Resource Controller Swap Extension comes with its price in
842 a bigger memory consumption. General purpose distribution kernels
843 which want to enable the feature but keep it disabled by default
844 and let the user enable it by swapaccount=1 boot command line
845 parameter should have this option unselected.
846 For those who want to have the feature enabled by default should
847 select this option (if, for some reason, they need to disable it
848 then swapaccount=0 does the trick).
852 depends on MEMCG && !SLOB
860 Generic block IO controller cgroup interface. This is the common
861 cgroup interface which should be used by various IO controlling
864 Currently, CFQ IO scheduler uses it to recognize task groups and
865 control disk bandwidth allocation (proportional time slice allocation)
866 to such task groups. It is also used by bio throttling logic in
867 block layer to implement upper limit in IO rates on a device.
869 This option only enables generic Block IO controller infrastructure.
870 One needs to also enable actual IO controlling logic/policy. For
871 enabling proportional weight division of disk bandwidth in CFQ, set
872 CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
873 CONFIG_BLK_DEV_THROTTLING=y.
875 See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.
877 config CGROUP_WRITEBACK
879 depends on MEMCG && BLK_CGROUP
882 menuconfig CGROUP_SCHED
883 bool "CPU controller"
886 This feature lets CPU scheduler recognize task groups and control CPU
887 bandwidth allocation to such task groups. It uses cgroups to group
891 config FAIR_GROUP_SCHED
892 bool "Group scheduling for SCHED_OTHER"
893 depends on CGROUP_SCHED
897 bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
898 depends on FAIR_GROUP_SCHED
901 This option allows users to define CPU bandwidth rates (limits) for
902 tasks running within the fair group scheduler. Groups with no limit
903 set are considered to be unconstrained and will run with no
905 See Documentation/scheduler/sched-bwc.rst for more information.
907 config RT_GROUP_SCHED
908 bool "Group scheduling for SCHED_RR/FIFO"
909 depends on CGROUP_SCHED
912 This feature lets you explicitly allocate real CPU bandwidth
913 to task groups. If enabled, it will also make it impossible to
914 schedule realtime tasks for non-root users until you allocate
915 realtime bandwidth for them.
916 See Documentation/scheduler/sched-rt-group.rst for more information.
920 config UCLAMP_TASK_GROUP
921 bool "Utilization clamping per group of tasks"
922 depends on CGROUP_SCHED
923 depends on UCLAMP_TASK
926 This feature enables the scheduler to track the clamped utilization
927 of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
929 When this option is enabled, the user can specify a min and max
930 CPU bandwidth which is allowed for each single task in a group.
931 The max bandwidth allows to clamp the maximum frequency a task
932 can use, while the min bandwidth allows to define a minimum
933 frequency a task will always use.
935 When task group based utilization clamping is enabled, an eventually
936 specified task-specific clamp value is constrained by the cgroup
937 specified clamp value. Both minimum and maximum task clamping cannot
938 be bigger than the corresponding clamping defined at task group level.
943 bool "PIDs controller"
945 Provides enforcement of process number limits in the scope of a
946 cgroup. Any attempt to fork more processes than is allowed in the
947 cgroup will fail. PIDs are fundamentally a global resource because it
948 is fairly trivial to reach PID exhaustion before you reach even a
949 conservative kmemcg limit. As a result, it is possible to grind a
950 system to halt without being limited by other cgroup policies. The
951 PIDs controller is designed to stop this from happening.
953 It should be noted that organisational operations (such as attaching
954 to a cgroup hierarchy) will *not* be blocked by the PIDs controller,
955 since the PIDs limit only affects a process's ability to fork, not to
959 bool "RDMA controller"
961 Provides enforcement of RDMA resources defined by IB stack.
962 It is fairly easy for consumers to exhaust RDMA resources, which
963 can result into resource unavailability to other consumers.
964 RDMA controller is designed to stop this from happening.
965 Attaching processes with active RDMA resources to the cgroup
966 hierarchy is allowed even if can cross the hierarchy's limit.
968 config CGROUP_FREEZER
969 bool "Freezer controller"
971 Provides a way to freeze and unfreeze all tasks in a
974 This option affects the ORIGINAL cgroup interface. The cgroup2 memory
975 controller includes important in-kernel memory consumers per default.
977 If you're using cgroup2, say N.
979 config CGROUP_HUGETLB
980 bool "HugeTLB controller"
981 depends on HUGETLB_PAGE
985 Provides a cgroup controller for HugeTLB pages.
986 When you enable this, you can put a per cgroup limit on HugeTLB usage.
987 The limit is enforced during page fault. Since HugeTLB doesn't
988 support page reclaim, enforcing the limit at page fault time implies
989 that, the application will get SIGBUS signal if it tries to access
990 HugeTLB pages beyond its limit. This requires the application to know
991 beforehand how much HugeTLB pages it would require for its use. The
992 control group is tracked in the third page lru pointer. This means
993 that we cannot use the controller with huge page less than 3 pages.
996 bool "Cpuset controller"
999 This option will let you create and manage CPUSETs which
1000 allow dynamically partitioning a system into sets of CPUs and
1001 Memory Nodes and assigning tasks to run only within those sets.
1002 This is primarily useful on large SMP or NUMA systems.
1006 config PROC_PID_CPUSET
1007 bool "Include legacy /proc/<pid>/cpuset file"
1011 config CGROUP_DEVICE
1012 bool "Device controller"
1014 Provides a cgroup controller implementing whitelists for
1015 devices which a process in the cgroup can mknod or open.
1017 config CGROUP_CPUACCT
1018 bool "Simple CPU accounting controller"
1020 Provides a simple controller for monitoring the
1021 total CPU consumed by the tasks in a cgroup.
1024 bool "Perf controller"
1025 depends on PERF_EVENTS
1027 This option extends the perf per-cpu mode to restrict monitoring
1028 to threads which belong to the cgroup specified and run on the
1034 bool "Support for eBPF programs attached to cgroups"
1035 depends on BPF_SYSCALL
1036 select SOCK_CGROUP_DATA
1038 Allow attaching eBPF programs to a cgroup using the bpf(2)
1039 syscall command BPF_PROG_ATTACH.
1041 In which context these programs are accessed depends on the type
1042 of attachment. For instance, programs that are attached using
1043 BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
1047 bool "Debug controller"
1049 depends on DEBUG_KERNEL
1051 This option enables a simple controller that exports
1052 debugging information about the cgroups framework. This
1053 controller is for control cgroup debugging only. Its
1054 interfaces are not stable.
1058 config SOCK_CGROUP_DATA
1064 menuconfig NAMESPACES
1065 bool "Namespaces support" if EXPERT
1066 depends on MULTIUSER
1069 Provides the way to make tasks work with different objects using
1070 the same id. For example same IPC id may refer to different objects
1071 or same user id or pid may refer to different tasks when used in
1072 different namespaces.
1077 bool "UTS namespace"
1080 In this namespace tasks see different info provided with the
1084 bool "IPC namespace"
1085 depends on (SYSVIPC || POSIX_MQUEUE)
1088 In this namespace tasks work with IPC ids which correspond to
1089 different IPC objects in different namespaces.
1092 bool "User namespace"
1095 This allows containers, i.e. vservers, to use user namespaces
1096 to provide different user info for different servers.
1098 When user namespaces are enabled in the kernel it is
1099 recommended that the MEMCG option also be enabled and that
1100 user-space use the memory control groups to limit the amount
1101 of memory a memory unprivileged users can use.
1106 bool "PID Namespaces"
1109 Support process id namespaces. This allows having multiple
1110 processes with the same pid as long as they are in different
1111 pid namespaces. This is a building block of containers.
1114 bool "Network namespace"
1118 Allow user space to create what appear to be multiple instances
1119 of the network stack.
1123 config CHECKPOINT_RESTORE
1124 bool "Checkpoint/restore support"
1125 select PROC_CHILDREN
1128 Enables additional kernel features in a sake of checkpoint/restore.
1129 In particular it adds auxiliary prctl codes to setup process text,
1130 data and heap segment sizes, and a few additional /proc filesystem
1133 If unsure, say N here.
1135 config SCHED_AUTOGROUP
1136 bool "Automatic process group scheduling"
1139 select FAIR_GROUP_SCHED
1141 This option optimizes the scheduler for common desktop workloads by
1142 automatically creating and populating task groups. This separation
1143 of workloads isolates aggressive CPU burners (like build jobs) from
1144 desktop applications. Task group autogeneration is currently based
1147 config SYSFS_DEPRECATED
1148 bool "Enable deprecated sysfs features to support old userspace tools"
1152 This option adds code that switches the layout of the "block" class
1153 devices, to not show up in /sys/class/block/, but only in
1156 This switch is only active when the sysfs.deprecated=1 boot option is
1157 passed or the SYSFS_DEPRECATED_V2 option is set.
1159 This option allows new kernels to run on old distributions and tools,
1160 which might get confused by /sys/class/block/. Since 2007/2008 all
1161 major distributions and tools handle this just fine.
1163 Recent distributions and userspace tools after 2009/2010 depend on
1164 the existence of /sys/class/block/, and will not work with this
1167 Only if you are using a new kernel on an old distribution, you might
1170 config SYSFS_DEPRECATED_V2
1171 bool "Enable deprecated sysfs features by default"
1174 depends on SYSFS_DEPRECATED
1176 Enable deprecated sysfs by default.
1178 See the CONFIG_SYSFS_DEPRECATED option for more details about this
1181 Only if you are using a new kernel on an old distribution, you might
1182 need to say Y here. Even then, odds are you would not need it
1183 enabled, you can always pass the boot option if absolutely necessary.
1186 bool "Kernel->user space relay support (formerly relayfs)"
1189 This option enables support for relay interface support in
1190 certain file systems (such as debugfs).
1191 It is designed to provide an efficient mechanism for tools and
1192 facilities to relay large amounts of data from kernel space to
1197 config BLK_DEV_INITRD
1198 bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
1200 The initial RAM filesystem is a ramfs which is loaded by the
1201 boot loader (loadlin or lilo) and that is mounted as root
1202 before the normal boot procedure. It is typically used to
1203 load modules needed to mount the "real" root file system,
1204 etc. See <file:Documentation/admin-guide/initrd.rst> for details.
1206 If RAM disk support (BLK_DEV_RAM) is also included, this
1207 also enables initial RAM disk (initrd) support and adds
1208 15 Kbytes (more on some other architectures) to the kernel size.
1214 source "usr/Kconfig"
1219 bool "Boot config support"
1220 depends on BLK_DEV_INITRD
1223 Extra boot config allows system admin to pass a config file as
1224 complemental extension of kernel cmdline when booting.
1225 The boot config file must be attached at the end of initramfs
1226 with checksum and size.
1227 See <file:Documentation/admin-guide/bootconfig.rst> for details.
1232 prompt "Compiler optimization level"
1233 default CC_OPTIMIZE_FOR_PERFORMANCE
1235 config CC_OPTIMIZE_FOR_PERFORMANCE
1236 bool "Optimize for performance (-O2)"
1238 This is the default optimization level for the kernel, building
1239 with the "-O2" compiler flag for best performance and most
1240 helpful compile-time warnings.
1242 config CC_OPTIMIZE_FOR_PERFORMANCE_O3
1243 bool "Optimize more for performance (-O3)"
1245 imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
1247 Choosing this option will pass "-O3" to your compiler to optimize
1248 the kernel yet more for performance.
1250 config CC_OPTIMIZE_FOR_SIZE
1251 bool "Optimize for size (-Os)"
1252 imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
1254 Choosing this option will pass "-Os" to your compiler resulting
1255 in a smaller kernel.
1259 config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1262 This requires that the arch annotates or otherwise protects
1263 its external entry points from being discarded. Linker scripts
1264 must also merge .text.*, .data.*, and .bss.* correctly into
1265 output sections. Care must be taken not to pull in unrelated
1266 sections (e.g., '.text.init'). Typically '.' in section names
1267 is used to distinguish them from label names / C identifiers.
1269 config LD_DEAD_CODE_DATA_ELIMINATION
1270 bool "Dead code and data elimination (EXPERIMENTAL)"
1271 depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
1273 depends on !(FUNCTION_TRACER && CC_IS_GCC && GCC_VERSION < 40800)
1274 depends on $(cc-option,-ffunction-sections -fdata-sections)
1275 depends on $(ld-option,--gc-sections)
1277 Enable this if you want to do dead code and data elimination with
1278 the linker by compiling with -ffunction-sections -fdata-sections,
1279 and linking with --gc-sections.
1281 This can reduce on disk and in-memory size of the kernel
1282 code and static data, particularly for small configs and
1283 on small systems. This has the possibility of introducing
1284 silently broken kernel if the required annotations are not
1285 present. This option is not well tested yet, so use at your
1294 config SYSCTL_EXCEPTION_TRACE
1297 Enable support for /proc/sys/debug/exception-trace.
1299 config SYSCTL_ARCH_UNALIGN_NO_WARN
1302 Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
1303 Allows arch to define/use @no_unaligned_warning to possibly warn
1304 about unaligned access emulation going on under the hood.
1306 config SYSCTL_ARCH_UNALIGN_ALLOW
1309 Enable support for /proc/sys/kernel/unaligned-trap
1310 Allows arches to define/use @unaligned_enabled to runtime toggle
1311 the unaligned access emulation.
1312 see arch/parisc/kernel/unaligned.c for reference
1314 config HAVE_PCSPKR_PLATFORM
1317 # interpreter that classic socket filters depend on
1322 bool "Configure standard kernel features (expert users)"
1323 # Unhide debug options, to make the on-by-default options visible
1326 This option allows certain base kernel options and settings
1327 to be disabled or tweaked. This is for specialized
1328 environments which can tolerate a "non-standard" kernel.
1329 Only use this if you really know what you are doing.
1332 bool "Enable 16-bit UID system calls" if EXPERT
1333 depends on HAVE_UID16 && MULTIUSER
1336 This enables the legacy 16-bit UID syscall wrappers.
1339 bool "Multiple users, groups and capabilities support" if EXPERT
1342 This option enables support for non-root users, groups and
1345 If you say N here, all processes will run with UID 0, GID 0, and all
1346 possible capabilities. Saying N here also compiles out support for
1347 system calls related to UIDs, GIDs, and capabilities, such as setuid,
1350 If unsure, say Y here.
1352 config SGETMASK_SYSCALL
1353 bool "sgetmask/ssetmask syscalls support" if EXPERT
1354 def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH
1356 sys_sgetmask and sys_ssetmask are obsolete system calls
1357 no longer supported in libc but still enabled by default in some
1360 If unsure, leave the default option here.
1362 config SYSFS_SYSCALL
1363 bool "Sysfs syscall support" if EXPERT
1366 sys_sysfs is an obsolete system call no longer supported in libc.
1367 Note that disabling this option is more secure but might break
1368 compatibility with some systems.
1370 If unsure say Y here.
1373 bool "open by fhandle syscalls" if EXPERT
1377 If you say Y here, a user level program will be able to map
1378 file names to handle and then later use the handle for
1379 different file system operations. This is useful in implementing
1380 userspace file servers, which now track files using handles instead
1381 of names. The handle would remain the same even if file names
1382 get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
1386 bool "Posix Clocks & timers" if EXPERT
1389 This includes native support for POSIX timers to the kernel.
1390 Some embedded systems have no use for them and therefore they
1391 can be configured out to reduce the size of the kernel image.
1393 When this option is disabled, the following syscalls won't be
1394 available: timer_create, timer_gettime: timer_getoverrun,
1395 timer_settime, timer_delete, clock_adjtime, getitimer,
1396 setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
1397 clock_getres and clock_nanosleep syscalls will be limited to
1398 CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
1404 bool "Enable support for printk" if EXPERT
1407 This option enables normal printk support. Removing it
1408 eliminates most of the message strings from the kernel image
1409 and makes the kernel more or less silent. As this makes it
1410 very difficult to diagnose system problems, saying N here is
1411 strongly discouraged.
1419 bool "BUG() support" if EXPERT
1422 Disabling this option eliminates support for BUG and WARN, reducing
1423 the size of your kernel image and potentially quietly ignoring
1424 numerous fatal conditions. You should only consider disabling this
1425 option for embedded systems with no facilities for reporting errors.
1431 bool "Enable ELF core dumps" if EXPERT
1433 Enable support for generating core dumps. Disabling saves about 4k.
1436 config PCSPKR_PLATFORM
1437 bool "Enable PC-Speaker support" if EXPERT
1438 depends on HAVE_PCSPKR_PLATFORM
1442 This option allows to disable the internal PC-Speaker
1443 support, saving some memory.
1447 bool "Enable full-sized data structures for core" if EXPERT
1449 Disabling this option reduces the size of miscellaneous core
1450 kernel data structures. This saves memory on small machines,
1451 but may reduce performance.
1454 bool "Enable futex support" if EXPERT
1458 Disabling this option will cause the kernel to be built without
1459 support for "fast userspace mutexes". The resulting kernel may not
1460 run glibc-based applications correctly.
1464 depends on FUTEX && RT_MUTEXES
1467 config HAVE_FUTEX_CMPXCHG
1471 Architectures should select this if futex_atomic_cmpxchg_inatomic()
1472 is implemented and always working. This removes a couple of runtime
1476 bool "Enable eventpoll support" if EXPERT
1479 Disabling this option will cause the kernel to be built without
1480 support for epoll family of system calls.
1483 bool "Enable signalfd() system call" if EXPERT
1486 Enable the signalfd() system call that allows to receive signals
1487 on a file descriptor.
1492 bool "Enable timerfd() system call" if EXPERT
1495 Enable the timerfd() system call that allows to receive timer
1496 events on a file descriptor.
1501 bool "Enable eventfd() system call" if EXPERT
1504 Enable the eventfd() system call that allows to receive both
1505 kernel notification (ie. KAIO) or userspace notifications.
1510 bool "Use full shmem filesystem" if EXPERT
1514 The shmem is an internal filesystem used to manage shared memory.
1515 It is backed by swap and manages resource limits. It is also exported
1516 to userspace as tmpfs if TMPFS is enabled. Disabling this
1517 option replaces shmem and tmpfs with the much simpler ramfs code,
1518 which may be appropriate on small systems without swap.
1521 bool "Enable AIO support" if EXPERT
1524 This option enables POSIX asynchronous I/O which may by used
1525 by some high performance threaded applications. Disabling
1526 this option saves about 7k.
1529 bool "Enable IO uring support" if EXPERT
1534 This option enables support for the io_uring interface, enabling
1535 applications to submit and complete IO through submission and
1536 completion rings that are shared between the kernel and application.
1538 config ADVISE_SYSCALLS
1539 bool "Enable madvise/fadvise syscalls" if EXPERT
1542 This option enables the madvise and fadvise syscalls, used by
1543 applications to advise the kernel about their future memory or file
1544 usage, improving performance. If building an embedded system where no
1545 applications use these syscalls, you can disable this option to save
1549 bool "Enable membarrier() system call" if EXPERT
1552 Enable the membarrier() system call that allows issuing memory
1553 barriers across all running threads, which can be used to distribute
1554 the cost of user-space memory barriers asymmetrically by transforming
1555 pairs of memory barriers into pairs consisting of membarrier() and a
1561 bool "Load all symbols for debugging/ksymoops" if EXPERT
1564 Say Y here to let the kernel print out symbolic crash information and
1565 symbolic stack backtraces. This increases the size of the kernel
1566 somewhat, as all symbols have to be loaded into the kernel image.
1569 bool "Include all symbols in kallsyms"
1570 depends on DEBUG_KERNEL && KALLSYMS
1572 Normally kallsyms only contains the symbols of functions for nicer
1573 OOPS messages and backtraces (i.e., symbols from the text and inittext
1574 sections). This is sufficient for most cases. And only in very rare
1575 cases (e.g., when a debugger is used) all symbols are required (e.g.,
1576 names of variables from the data sections, etc).
1578 This option makes sure that all symbols are loaded into the kernel
1579 image (i.e., symbols from all sections) in cost of increased kernel
1580 size (depending on the kernel configuration, it may be 300KiB or
1581 something like this).
1583 Say N unless you really need all symbols.
1585 config KALLSYMS_ABSOLUTE_PERCPU
1588 default X86_64 && SMP
1590 config KALLSYMS_BASE_RELATIVE
1595 Instead of emitting them as absolute values in the native word size,
1596 emit the symbol references in the kallsyms table as 32-bit entries,
1597 each containing a relative value in the range [base, base + U32_MAX]
1598 or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
1599 an absolute value in the range [0, S32_MAX] or a relative value in the
1600 range [base, base + S32_MAX], where base is the lowest relative symbol
1601 address encountered in the image.
1603 On 64-bit builds, this reduces the size of the address table by 50%,
1604 but more importantly, it results in entries whose values are build
1605 time constants, and no relocation pass is required at runtime to fix
1606 up the entries based on the runtime load address of the kernel.
1608 # end of the "standard kernel features (expert users)" menu
1610 # syscall, maps, verifier
1612 bool "Enable bpf() system call"
1617 Enable the bpf() system call that allows to manipulate eBPF
1618 programs and maps via file descriptors.
1620 config BPF_JIT_ALWAYS_ON
1621 bool "Permanently enable BPF JIT and remove BPF interpreter"
1622 depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT
1624 Enables BPF JIT and removes BPF interpreter to avoid
1625 speculative execution of BPF instructions by the interpreter
1628 bool "Enable userfaultfd() system call"
1631 Enable the userfaultfd() system call that allows to intercept and
1632 handle page faults in userland.
1634 config ARCH_HAS_MEMBARRIER_CALLBACKS
1637 config ARCH_HAS_MEMBARRIER_SYNC_CORE
1641 bool "Enable rseq() system call" if EXPERT
1643 depends on HAVE_RSEQ
1646 Enable the restartable sequences system call. It provides a
1647 user-space cache for the current CPU number value, which
1648 speeds up getting the current CPU number from user-space,
1649 as well as an ABI to speed up user-space operations on
1656 bool "Enabled debugging of rseq() system call" if EXPERT
1657 depends on RSEQ && DEBUG_KERNEL
1659 Enable extra debugging checks for the rseq system call.
1664 bool "Embedded system"
1665 option allnoconfig_y
1668 This option should be enabled if compiling the kernel for
1669 an embedded system so certain expert options are available
1672 config HAVE_PERF_EVENTS
1675 See tools/perf/design.txt for details.
1677 config PERF_USE_VMALLOC
1680 See tools/perf/design.txt for details
1683 bool "PC/104 support" if EXPERT
1685 Expose PC/104 form factor device drivers and options available for
1686 selection and configuration. Enable this option if your target
1687 machine has a PC/104 bus.
1689 menu "Kernel Performance Events And Counters"
1692 bool "Kernel performance events and counters"
1693 default y if PROFILING
1694 depends on HAVE_PERF_EVENTS
1698 Enable kernel support for various performance events provided
1699 by software and hardware.
1701 Software events are supported either built-in or via the
1702 use of generic tracepoints.
1704 Most modern CPUs support performance events via performance
1705 counter registers. These registers count the number of certain
1706 types of hw events: such as instructions executed, cachemisses
1707 suffered, or branches mis-predicted - without slowing down the
1708 kernel or applications. These registers can also trigger interrupts
1709 when a threshold number of events have passed - and can thus be
1710 used to profile the code that runs on that CPU.
1712 The Linux Performance Event subsystem provides an abstraction of
1713 these software and hardware event capabilities, available via a
1714 system call and used by the "perf" utility in tools/perf/. It
1715 provides per task and per CPU counters, and it provides event
1716 capabilities on top of those.
1720 config DEBUG_PERF_USE_VMALLOC
1722 bool "Debug: use vmalloc to back perf mmap() buffers"
1723 depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
1724 select PERF_USE_VMALLOC
1726 Use vmalloc memory to back perf mmap() buffers.
1728 Mostly useful for debugging the vmalloc code on platforms
1729 that don't require it.
1735 config VM_EVENT_COUNTERS
1737 bool "Enable VM event counters for /proc/vmstat" if EXPERT
1739 VM event counters are needed for event counts to be shown.
1740 This option allows the disabling of the VM event counters
1741 on EXPERT systems. /proc/vmstat will only show page counts
1742 if VM event counters are disabled.
1746 bool "Enable SLUB debugging support" if EXPERT
1747 depends on SLUB && SYSFS
1749 SLUB has extensive debug support features. Disabling these can
1750 result in significant savings in code size. This also disables
1751 SLUB sysfs support. /sys/slab will not exist and there will be
1752 no support for cache validation etc.
1754 config SLUB_MEMCG_SYSFS_ON
1756 bool "Enable memcg SLUB sysfs support by default" if EXPERT
1757 depends on SLUB && SYSFS && MEMCG
1759 SLUB creates a directory under /sys/kernel/slab for each
1760 allocation cache to host info and debug files. If memory
1761 cgroup is enabled, each cache can have per memory cgroup
1762 caches. SLUB can create the same sysfs directories for these
1763 caches under /sys/kernel/slab/CACHE/cgroup but it can lead
1764 to a very high number of debug files being created. This is
1765 controlled by slub_memcg_sysfs boot parameter and this
1766 config option determines the parameter's default value.
1769 bool "Disable heap randomization"
1772 Randomizing heap placement makes heap exploits harder, but it
1773 also breaks ancient binaries (including anything libc5 based).
1774 This option changes the bootup default to heap randomization
1775 disabled, and can be overridden at runtime by setting
1776 /proc/sys/kernel/randomize_va_space to 2.
1778 On non-ancient distros (post-2000 ones) N is usually a safe choice.
1781 prompt "Choose SLAB allocator"
1784 This option allows to select a slab allocator.
1788 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1790 The regular slab allocator that is established and known to work
1791 well in all environments. It organizes cache hot objects in
1792 per cpu and per node queues.
1795 bool "SLUB (Unqueued Allocator)"
1796 select HAVE_HARDENED_USERCOPY_ALLOCATOR
1798 SLUB is a slab allocator that minimizes cache line usage
1799 instead of managing queues of cached objects (SLAB approach).
1800 Per cpu caching is realized using slabs of objects instead
1801 of queues of objects. SLUB can use memory efficiently
1802 and has enhanced diagnostics. SLUB is the default choice for
1807 bool "SLOB (Simple Allocator)"
1809 SLOB replaces the stock allocator with a drastically simpler
1810 allocator. SLOB is generally more space efficient but
1811 does not perform as well on large systems.
1815 config SLAB_MERGE_DEFAULT
1816 bool "Allow slab caches to be merged"
1819 For reduced kernel memory fragmentation, slab caches can be
1820 merged when they share the same size and other characteristics.
1821 This carries a risk of kernel heap overflows being able to
1822 overwrite objects from merged caches (and more easily control
1823 cache layout), which makes such heap attacks easier to exploit
1824 by attackers. By keeping caches unmerged, these kinds of exploits
1825 can usually only damage objects in the same cache. To disable
1826 merging at runtime, "slab_nomerge" can be passed on the kernel
1829 config SLAB_FREELIST_RANDOM
1831 depends on SLAB || SLUB
1832 bool "SLAB freelist randomization"
1834 Randomizes the freelist order used on creating new pages. This
1835 security feature reduces the predictability of the kernel slab
1836 allocator against heap overflows.
1838 config SLAB_FREELIST_HARDENED
1839 bool "Harden slab freelist metadata"
1842 Many kernel heap attacks try to target slab cache metadata and
1843 other infrastructure. This options makes minor performance
1844 sacrifices to harden the kernel slab allocator against common
1845 freelist exploit methods.
1847 config SHUFFLE_PAGE_ALLOCATOR
1848 bool "Page allocator randomization"
1849 default SLAB_FREELIST_RANDOM && ACPI_NUMA
1851 Randomization of the page allocator improves the average
1852 utilization of a direct-mapped memory-side-cache. See section
1853 5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI
1854 6.2a specification for an example of how a platform advertises
1855 the presence of a memory-side-cache. There are also incidental
1856 security benefits as it reduces the predictability of page
1857 allocations to compliment SLAB_FREELIST_RANDOM, but the
1858 default granularity of shuffling on the "MAX_ORDER - 1" i.e,
1859 10th order of pages is selected based on cache utilization
1862 While the randomization improves cache utilization it may
1863 negatively impact workloads on platforms without a cache. For
1864 this reason, by default, the randomization is enabled only
1865 after runtime detection of a direct-mapped memory-side-cache.
1866 Otherwise, the randomization may be force enabled with the
1867 'page_alloc.shuffle' kernel command line parameter.
1871 config SLUB_CPU_PARTIAL
1873 depends on SLUB && SMP
1874 bool "SLUB per cpu partial cache"
1876 Per cpu partial caches accelerate objects allocation and freeing
1877 that is local to a processor at the price of more indeterminism
1878 in the latency of the free. On overflow these caches will be cleared
1879 which requires the taking of locks that may cause latency spikes.
1880 Typically one would choose no for a realtime system.
1882 config MMAP_ALLOW_UNINITIALIZED
1883 bool "Allow mmapped anonymous memory to be uninitialized"
1884 depends on EXPERT && !MMU
1887 Normally, and according to the Linux spec, anonymous memory obtained
1888 from mmap() has its contents cleared before it is passed to
1889 userspace. Enabling this config option allows you to request that
1890 mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
1891 providing a huge performance boost. If this option is not enabled,
1892 then the flag will be ignored.
1894 This is taken advantage of by uClibc's malloc(), and also by
1895 ELF-FDPIC binfmt's brk and stack allocator.
1897 Because of the obvious security issues, this option should only be
1898 enabled on embedded devices where you control what is run in
1899 userspace. Since that isn't generally a problem on no-MMU systems,
1900 it is normally safe to say Y here.
1902 See Documentation/nommu-mmap.txt for more information.
1904 config SYSTEM_DATA_VERIFICATION
1906 select SYSTEM_TRUSTED_KEYRING
1910 select ASYMMETRIC_KEY_TYPE
1911 select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
1914 select X509_CERTIFICATE_PARSER
1915 select PKCS7_MESSAGE_PARSER
1917 Provide PKCS#7 message verification using the contents of the system
1918 trusted keyring to provide public keys. This then can be used for
1919 module verification, kexec image verification and firmware blob
1923 bool "Profiling support"
1925 Say Y here to enable the extended profiling support mechanisms used
1926 by profilers such as OProfile.
1929 # Place an empty function call at each tracepoint site. Can be
1930 # dynamically changed for a probe function.
1935 endmenu # General setup
1937 source "arch/Kconfig"
1944 default 0 if BASE_FULL
1945 default 1 if !BASE_FULL
1947 config MODULE_SIG_FORMAT
1949 select SYSTEM_DATA_VERIFICATION
1952 bool "Enable loadable module support"
1955 Kernel modules are small pieces of compiled code which can
1956 be inserted in the running kernel, rather than being
1957 permanently built into the kernel. You use the "modprobe"
1958 tool to add (and sometimes remove) them. If you say Y here,
1959 many parts of the kernel can be built as modules (by
1960 answering M instead of Y where indicated): this is most
1961 useful for infrequently used options which are not required
1962 for booting. For more information, see the man pages for
1963 modprobe, lsmod, modinfo, insmod and rmmod.
1965 If you say Y here, you will need to run "make
1966 modules_install" to put the modules under /lib/modules/
1967 where modprobe can find them (you may need to be root to do
1974 config MODULE_FORCE_LOAD
1975 bool "Forced module loading"
1978 Allow loading of modules without version information (ie. modprobe
1979 --force). Forced module loading sets the 'F' (forced) taint flag and
1980 is usually a really bad idea.
1982 config MODULE_UNLOAD
1983 bool "Module unloading"
1985 Without this option you will not be able to unload any
1986 modules (note that some modules may not be unloadable
1987 anyway), which makes your kernel smaller, faster
1988 and simpler. If unsure, say Y.
1990 config MODULE_FORCE_UNLOAD
1991 bool "Forced module unloading"
1992 depends on MODULE_UNLOAD
1994 This option allows you to force a module to unload, even if the
1995 kernel believes it is unsafe: the kernel will remove the module
1996 without waiting for anyone to stop using it (using the -f option to
1997 rmmod). This is mainly for kernel developers and desperate users.
2001 bool "Module versioning support"
2003 Usually, you have to use modules compiled with your kernel.
2004 Saying Y here makes it sometimes possible to use modules
2005 compiled for different kernels, by adding enough information
2006 to the modules to (hopefully) spot any changes which would
2007 make them incompatible with the kernel you are running. If
2010 config ASM_MODVERSIONS
2012 default HAVE_ASM_MODVERSIONS && MODVERSIONS
2014 This enables module versioning for exported symbols also from
2015 assembly. This can be enabled only when the target architecture
2018 config MODULE_REL_CRCS
2020 depends on MODVERSIONS
2022 config MODULE_SRCVERSION_ALL
2023 bool "Source checksum for all modules"
2025 Modules which contain a MODULE_VERSION get an extra "srcversion"
2026 field inserted into their modinfo section, which contains a
2027 sum of the source files which made it. This helps maintainers
2028 see exactly which source was used to build a module (since
2029 others sometimes change the module source without updating
2030 the version). With this option, such a "srcversion" field
2031 will be created for all modules. If unsure, say N.
2034 bool "Module signature verification"
2035 select MODULE_SIG_FORMAT
2037 Check modules for valid signatures upon load: the signature
2038 is simply appended to the module. For more information see
2039 <file:Documentation/admin-guide/module-signing.rst>.
2041 Note that this option adds the OpenSSL development packages as a
2042 kernel build dependency so that the signing tool can use its crypto
2045 You should enable this option if you wish to use either
2046 CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
2047 another LSM - otherwise unsigned modules will be loadable regardless
2048 of the lockdown policy.
2050 !!!WARNING!!! If you enable this option, you MUST make sure that the
2051 module DOES NOT get stripped after being signed. This includes the
2052 debuginfo strip done by some packagers (such as rpmbuild) and
2053 inclusion into an initramfs that wants the module size reduced.
2055 config MODULE_SIG_FORCE
2056 bool "Require modules to be validly signed"
2057 depends on MODULE_SIG
2059 Reject unsigned modules or signed modules for which we don't have a
2060 key. Without this, such modules will simply taint the kernel.
2062 config MODULE_SIG_ALL
2063 bool "Automatically sign all modules"
2065 depends on MODULE_SIG
2067 Sign all modules during make modules_install. Without this option,
2068 modules must be signed manually, using the scripts/sign-file tool.
2070 comment "Do not forget to sign required modules with scripts/sign-file"
2071 depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
2074 prompt "Which hash algorithm should modules be signed with?"
2075 depends on MODULE_SIG
2077 This determines which sort of hashing algorithm will be used during
2078 signature generation. This algorithm _must_ be built into the kernel
2079 directly so that signature verification can take place. It is not
2080 possible to load a signed module containing the algorithm to check
2081 the signature on that module.
2083 config MODULE_SIG_SHA1
2084 bool "Sign modules with SHA-1"
2087 config MODULE_SIG_SHA224
2088 bool "Sign modules with SHA-224"
2089 select CRYPTO_SHA256
2091 config MODULE_SIG_SHA256
2092 bool "Sign modules with SHA-256"
2093 select CRYPTO_SHA256
2095 config MODULE_SIG_SHA384
2096 bool "Sign modules with SHA-384"
2097 select CRYPTO_SHA512
2099 config MODULE_SIG_SHA512
2100 bool "Sign modules with SHA-512"
2101 select CRYPTO_SHA512
2105 config MODULE_SIG_HASH
2107 depends on MODULE_SIG
2108 default "sha1" if MODULE_SIG_SHA1
2109 default "sha224" if MODULE_SIG_SHA224
2110 default "sha256" if MODULE_SIG_SHA256
2111 default "sha384" if MODULE_SIG_SHA384
2112 default "sha512" if MODULE_SIG_SHA512
2114 config MODULE_COMPRESS
2115 bool "Compress modules on installation"
2118 Compresses kernel modules when 'make modules_install' is run; gzip or
2119 xz depending on "Compression algorithm" below.
2121 module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
2123 Out-of-tree kernel modules installed using Kbuild will also be
2124 compressed upon installation.
2126 Note: for modules inside an initrd or initramfs, it's more efficient
2127 to compress the whole initrd or initramfs instead.
2129 Note: This is fully compatible with signed modules.
2134 prompt "Compression algorithm"
2135 depends on MODULE_COMPRESS
2136 default MODULE_COMPRESS_GZIP
2138 This determines which sort of compression will be used during
2139 'make modules_install'.
2141 GZIP (default) and XZ are supported.
2143 config MODULE_COMPRESS_GZIP
2146 config MODULE_COMPRESS_XZ
2151 config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
2152 bool "Allow loading of modules with missing namespace imports"
2154 Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in
2155 a namespace. A module that makes use of a symbol exported with such a
2156 namespace is required to import the namespace via MODULE_IMPORT_NS().
2157 There is no technical reason to enforce correct namespace imports,
2158 but it creates consistency between symbols defining namespaces and
2159 users importing namespaces they make use of. This option relaxes this
2160 requirement and lifts the enforcement when loading a module.
2164 config UNUSED_SYMBOLS
2165 bool "Enable unused/obsolete exported symbols"
2168 Unused but exported symbols make the kernel needlessly bigger. For
2169 that reason most of these unused exports will soon be removed. This
2170 option is provided temporarily to provide a transition period in case
2171 some external kernel module needs one of these symbols anyway. If you
2172 encounter such a case in your module, consider if you are actually
2173 using the right API. (rationale: since nobody in the kernel is using
2174 this in a module, there is a pretty good chance it's actually the
2175 wrong interface to use). If you really need the symbol, please send a
2176 mail to the linux kernel mailing list mentioning the symbol and why
2177 you really need it, and what the merge plan to the mainline kernel for
2180 config TRIM_UNUSED_KSYMS
2181 bool "Trim unused exported kernel symbols"
2182 depends on !UNUSED_SYMBOLS
2184 The kernel and some modules make many symbols available for
2185 other modules to use via EXPORT_SYMBOL() and variants. Depending
2186 on the set of modules being selected in your kernel configuration,
2187 many of those exported symbols might never be used.
2189 This option allows for unused exported symbols to be dropped from
2190 the build. In turn, this provides the compiler more opportunities
2191 (especially when using LTO) for optimizing the code and reducing
2192 binary size. This might have some security advantages as well.
2194 If unsure, or if you need to build out-of-tree modules, say N.
2198 config MODULES_TREE_LOOKUP
2200 depends on PERF_EVENTS || TRACING
2202 config INIT_ALL_POSSIBLE
2205 Back when each arch used to define their own cpu_online_mask and
2206 cpu_possible_mask, some of them chose to initialize cpu_possible_mask
2207 with all 1s, and others with all 0s. When they were centralised,
2208 it was better to provide this option than to break all the archs
2209 and have several arch maintainers pursuing me down dark alleys.
2211 source "block/Kconfig"
2213 config PREEMPT_NOTIFIERS
2223 Build a simple ASN.1 grammar compiler that produces a bytecode output
2224 that can be interpreted by the ASN.1 stream decoder and used to
2225 inform it as to what tags are to be expected in a stream and what
2226 functions to call on what tags.
2228 source "kernel/Kconfig.locks"
2230 config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
2233 # It may be useful for an architecture to override the definitions of the
2234 # SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in <linux/syscalls.h>
2235 # and the COMPAT_ variants in <linux/compat.h>, in particular to use a
2236 # different calling convention for syscalls. They can also override the
2237 # macros for not-implemented syscalls in kernel/sys_ni.c and
2238 # kernel/time/posix-stubs.c. All these overrides need to be available in
2239 # <asm/syscall_wrapper.h>.
2240 config ARCH_HAS_SYSCALL_WRAPPER
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