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Johannes Weiner ead87f1165 kernel: sysctl: make drop_caches write-only 
[ Upstream commit 204cb79ad4 ]

Currently, the drop_caches proc file and sysctl read back the last value
written, suggesting this is somehow a stateful setting instead of a
one-time command.  Make it write-only, like e.g.  compact_memory.

While mitigating a VM problem at scale in our fleet, there was confusion
about whether writing to this file will permanently switch the kernel into
a non-caching mode.  This influences the decision making in a tense
situation, where tens of people are trying to fix tens of thousands of
affected machines: Do we need a rollback strategy?  What are the
performance implications of operating in a non-caching state for several
days?  It also caused confusion when the kernel team said we may need to
write the file several times to make sure it's effective ("But it already
reads back 3?").

Link: http://lkml.kernel.org/r/20191031221602.9375-1-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Chris Down <chris@chrisdown.name>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2020-01-04 19:18:32 +01:00
..
bpf bpf: Provide better register bounds after jmp32 instructions 2019-12-31 16:45:48 +01:00
cgroup cgroup: freezer: don't change task and cgroups status unnecessarily 2019-12-31 16:45:06 +01:00
configs kvm_config: add CONFIG_VIRTIO_MENU 2018-10-24 20:55:56 -04:00
debug kgdb: don't use a notifier to enter kgdb at panic; call directly 2019-09-25 17:51:40 -07:00
dma dma-mapping: fix handling of dma-ranges for reserved memory (again) 2020-01-04 19:17:00 +01:00
events perf/core: Fix the mlock accounting, again 2019-12-31 16:45:38 +01:00
gcov um: Enable CONFIG_CONSTRUCTORS 2019-09-15 21:37:13 +02:00
irq irq/irqdomain: Update __irq_domain_alloc_fwnode() function documentation 2019-11-05 00:48:26 +01:00
livepatch livepatch: Nullify obj->mod in klp_module_coming()'s error path 2019-08-19 13:03:37 +02:00
locking Revert "locking/pvqspinlock: Don't wait if vCPU is preempted" 2019-09-25 10:22:37 +02:00
power PM: QoS: Invalidate frequency QoS requests after removal 2019-11-20 10:46:42 +01:00
printk Merge branch 'for-5.4' into for-linus 2019-09-16 12:54:25 +02:00
rcu Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-09-16 17:25:49 -07:00
sched cpufreq: Avoid leaving stale IRQ work items during CPU offline 2019-12-31 16:46:06 +01:00
time time: Zero the upper 32-bits in __kernel_timespec on 32-bit 2019-12-13 08:42:18 +01:00
trace tracing/kprobe: Check whether the non-suffixed symbol is notrace 2019-12-31 16:45:29 +01:00
.gitignore Provide in-kernel headers to make extending kernel easier 2019-04-29 16:48:03 +02:00
Kconfig.freezer treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.hz treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.locks treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Kconfig.preempt sched/rt, Kconfig: Unbreak def/oldconfig with CONFIG_PREEMPT=y 2019-07-22 18:05:11 +02:00
Makefile Merge branch 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity 2019-09-27 19:37:27 -07:00
acct.c acct_on(): don't mess with freeze protection 2019-04-04 21:04:13 -04:00
async.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
audit.c audit/stable-5.3 PR 20190702 2019-07-08 18:55:42 -07:00
audit.h audit/stable-5.3 PR 20190702 2019-07-08 18:55:42 -07:00
audit_fsnotify.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
audit_tree.c fsnotify: switch send_to_group() and ->handle_event to const struct qstr * 2019-04-26 13:51:03 -04:00
audit_watch.c audit_get_nd(): don't unlock parent too early 2019-11-10 11:56:55 -05:00
auditfilter.c audit/stable-5.3 PR 20190702 2019-07-08 18:55:42 -07:00
auditsc.c audit: enforce op for string fields 2019-05-28 17:46:43 -04:00
backtracetest.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
bounds.c kbuild: fix kernel/bounds.c 'W=1' warning 2018-10-31 08:54:14 -07:00
capability.c LSM: add SafeSetID module that gates setid calls 2019-01-25 11:22:43 -08:00
compat.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500 2019-06-19 17:09:55 +02:00
configs.c kernel/configs: Replace GPL boilerplate code with SPDX identifier 2019-07-30 18:34:15 +02:00
context_tracking.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
cpu.c cpu/speculation: Uninline and export CPU mitigations helpers 2019-11-04 12:22:02 +01:00
cpu_pm.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 282 2019-06-05 17:36:37 +02:00
crash_core.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 230 2019-06-19 17:09:06 +02:00
crash_dump.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
cred.c Merge branch 'access-creds' 2019-07-25 08:36:29 -07:00
delayacct.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 25 2019-05-21 11:52:39 +02:00
dma.c
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elfcore.c kernel/elfcore.c: include proper prototypes 2019-09-25 17:51:39 -07:00
exec_domain.c
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exit.c futex: Mark the begin of futex exit explicitly 2019-11-29 10:10:11 +01:00
extable.c extable: Add function to search only kernel exception table 2019-08-21 22:23:48 +10:00
fail_function.c fail_function: no need to check return value of debugfs_create functions 2019-06-03 15:49:06 +02:00
fork.c futex: Split futex_mm_release() for exit/exec 2019-11-29 10:10:10 +01:00
freezer.c Revert "libata, freezer: avoid block device removal while system is frozen" 2019-10-06 09:11:37 -06:00
futex.c futex: Prevent exit livelock 2019-11-29 10:10:14 +01:00
gen_kheaders.sh kheaders: substituting --sort in archive creation 2019-10-17 09:08:19 +09:00
groups.c
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hung_task.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
iomem.c mm/nvdimm: add is_ioremap_addr and use that to check ioremap address 2019-07-12 11:05:40 -07:00
irq_work.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
jump_label.c jump_label: Don't warn on __exit jump entries 2019-08-29 15:10:10 +01:00
kallsyms.c kallsyms: Don't let kallsyms_lookup_size_offset() fail on retrieving the first symbol 2019-08-27 16:19:56 +01:00
kcmp.c
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kcov.c kcov: convert kcov.refcount to refcount_t 2019-03-07 18:32:02 -08:00
kexec.c kexec_load: Disable at runtime if the kernel is locked down 2019-08-19 21:54:15 -07:00
kexec_core.c kexec: bail out upon SIGKILL when allocating memory. 2019-09-25 17:51:40 -07:00
kexec_elf.c kexec_elf: support 32 bit ELF files 2019-09-06 23:58:44 +02:00
kexec_file.c Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
kexec_internal.h
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kheaders.c kheaders: Move from proc to sysfs 2019-05-24 20:16:01 +02:00
kmod.c
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kprobes.c Tracing updates: 2019-09-20 11:19:48 -07:00
ksysfs.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 170 2019-05-30 11:26:39 -07:00
kthread.c kthread: make __kthread_queue_delayed_work static 2019-10-16 09:20:58 -07:00
latencytop.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
module-internal.h treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
module.c Merge branch 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-09-28 08:14:15 -07:00
module_signature.c MODSIGN: Export module signature definitions 2019-08-05 18:39:56 -04:00
module_signing.c MODSIGN: Export module signature definitions 2019-08-05 18:39:56 -04:00
notifier.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
nsproxy.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
padata.c padata: remove cpu_index from the parallel_queue 2019-09-13 21:15:41 +10:00
panic.c panic: ensure preemption is disabled during panic() 2019-10-07 15:47:19 -07:00
params.c lockdown: Lock down module params that specify hardware parameters (eg. ioport) 2019-08-19 21:54:16 -07:00
pid.c kernel/pid.c: convert struct pid count to refcount_t 2019-07-16 19:23:24 -07:00
pid_namespace.c proc/sysctl: add shared variables for range check 2019-07-18 17:08:07 -07:00
profile.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
ptrace.c ptrace: add PTRACE_GET_SYSCALL_INFO request 2019-07-16 19:23:24 -07:00
range.c
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reboot.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
relay.c Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-03-12 13:27:20 -07:00
resource.c mm/memory_hotplug.c: use PFN_UP / PFN_DOWN in walk_system_ram_range() 2019-09-24 15:54:09 -07:00
rseq.c signal: Remove task parameter from force_sig 2019-05-27 09:36:28 -05:00
seccomp.c signal: Remove the signal number and task parameters from force_sig_info 2019-05-29 09:31:44 -05:00
signal.c cgroup: freezer: call cgroup_enter_frozen() with preemption disabled in ptrace_stop() 2019-10-11 08:39:57 -07:00
smp.c smp: Warn on function calls from softirq context 2019-07-20 11:27:16 +02:00
smpboot.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
smpboot.h
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softirq.c Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-07-08 11:01:13 -07:00
stackleak.c stackleak: Mark stackleak_track_stack() as notrace 2018-12-05 19:31:44 -08:00
stacktrace.c stacktrace: Don't skip first entry on noncurrent tasks 2019-11-04 21:19:25 +01:00
stop_machine.c stop_machine: Avoid potential race behaviour 2019-10-17 12:47:12 +02:00
sys.c Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-09-17 12:35:15 -07:00
sys_ni.c arch: handle arches who do not yet define clone3 2019-06-21 01:54:53 +02:00
sysctl.c kernel: sysctl: make drop_caches write-only 2020-01-04 19:18:32 +01:00
sysctl_binary.c kernel/sysctl: add panic_print into sysctl 2019-01-04 13:13:47 -08:00
task_work.c
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taskstats.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
test_kprobes.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 25 2019-05-21 11:52:39 +02:00
torture.c torture: Remove exporting of internal functions 2019-08-01 14:30:22 -07:00
tracepoint.c The main changes in this release include: 2019-07-18 11:51:00 -07:00
tsacct.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 157 2019-05-30 11:26:37 -07:00
ucount.c proc/sysctl: add shared variables for range check 2019-07-18 17:08:07 -07:00
uid16.c
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uid16.h
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umh.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
up.c smp: Remove smp_call_function() and on_each_cpu() return values 2019-06-23 14:26:26 +02:00
user-return-notifier.c treewide: Add SPDX license identifier for missed files 2019-05-21 10:50:45 +02:00
user.c Keyrings namespacing 2019-07-08 19:36:47 -07:00
user_namespace.c Keyrings namespacing 2019-07-08 19:36:47 -07:00
utsname.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
utsname_sysctl.c treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441 2019-06-05 17:37:17 +02:00
watchdog.c watchdog: Mark watchdog_hrtimer to expire in hard interrupt context 2019-08-01 20:51:20 +02:00
watchdog_hld.c kernel/watchdog_hld.c: hard lockup message should end with a newline 2019-04-19 09:46:05 -07:00
workqueue.c workqueue: Fix missing kfree(rescuer) in destroy_workqueue() 2019-12-17 19:56:54 +01:00
workqueue_internal.h sched/core, workqueues: Distangle worker accounting from rq lock 2019-04-16 16:55:15 +02:00