David Rientjes 89e8a244b9 cpusets: avoid looping when storing to mems_allowed if one node remains set ... {get,put}_mems_allowed() exist so that general kernel code may locklessly access a task's set of allowable nodes without having the chance that a concurrent write will cause the nodemask to be empty on configurations where MAX_NUMNODES > BITS_PER_LONG. This could incur a significant delay, however, especially in low memory conditions because the page allocator is blocking and reclaim requires get_mems_allowed() itself. It is not atypical to see writes to cpuset.mems take over 2 seconds to complete, for example. In low memory conditions, this is problematic because it's one of the most imporant times to change cpuset.mems in the first place! The only way a task's set of allowable nodes may change is through cpusets by writing to cpuset.mems and when attaching a task to a generic code is not reading the nodemask with get_mems_allowed() at the same time, and then clearing all the old nodes. This prevents the possibility that a reader will see an empty nodemask at the same time the writer is storing a new nodemask. If at least one node remains unchanged, though, it's possible to simply set all new nodes and then clear all the old nodes. Changing a task's nodemask is protected by cgroup_mutex so it's guaranteed that two threads are not changing the same task's nodemask at the same time, so the nodemask is guaranteed to be stored before another thread changes it and determines whether a node remains set or not. Signed-off-by: David Rientjes <rientjes@google.com> Cc: Miao Xie <miaox@cn.fujitsu.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Nick Piggin <npiggin@kernel.dk> Cc: Paul Menage <paul@paulmenage.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2011-11-02 16:07:00 -07:00
..
debug	kgdb: follow rename pack_hex_byte() to hex_byte_pack()	2011-10-31 17:30:56 -07:00
events	mm: distinguish between mlocked and pinned pages	2011-10-31 17:30:46 -07:00
gcov
irq	Merge branch 'next/dt' of git://git.linaro.org/people/arnd/arm-soc	2011-11-01 21:02:35 -07:00
power
time
trace
.gitignore
acct.c
async.c
audit_tree.c
audit_watch.c
audit.c
audit.h
auditfilter.c
auditsc.c
backtracetest.c
bounds.c
capability.c
cgroup_freezer.c
cgroup.c	cgroups: don't attach task to subsystem if migration failed	2011-11-02 16:06:59 -07:00
compat.c
configs.c
cpu_pm.c
cpu.c
cpuset.c	cpusets: avoid looping when storing to mems_allowed if one node remains set	2011-11-02 16:07:00 -07:00
crash_dump.c
cred.c
delayacct.c
dma.c
elfcore.c
exec_domain.c
exit.c	oom: remove oom_disable_count	2011-10-31 17:30:45 -07:00
extable.c
fork.c	oom: remove oom_disable_count	2011-10-31 17:30:45 -07:00
freezer.c
futex_compat.c
futex.c
groups.c
hrtimer.c
hung_task.c
irq_work.c
itimer.c
jump_label.c
kallsyms.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kexec.c
kfifo.c
kmod.c
kprobes.c
ksysfs.c
kthread.c
latencytop.c
lockdep_internals.h
lockdep_proc.c
lockdep_states.h
lockdep.c
Makefile
module.c
mutex-debug.c
mutex-debug.h
mutex.c
mutex.h
notifier.c
nsproxy.c
padata.c
panic.c
params.c
pid_namespace.c
pid.c
posix-cpu-timers.c
posix-timers.c
printk.c	printk: remove bounds checking for log_prefix	2011-10-31 17:30:53 -07:00
profile.c
ptrace.c
range.c
rcu.h
rcupdate.c
rcutiny_plugin.h
rcutiny.c
rcutorture.c
rcutree_plugin.h
rcutree_trace.c
rcutree.c
rcutree.h
relay.c
res_counter.c
resource.c
rtmutex_common.h
rtmutex-debug.c
rtmutex-debug.h
rtmutex-tester.c
rtmutex.c
rtmutex.h
rwsem.c
sched_autogroup.c
sched_autogroup.h
sched_clock.c
sched_cpupri.c
sched_cpupri.h
sched_debug.c
sched_fair.c
sched_features.h
sched_idletask.c
sched_rt.c
sched_stats.h
sched_stoptask.c
sched.c
seccomp.c
semaphore.c
signal.c
smp.c
softirq.c
spinlock.c
srcu.c
stacktrace.c
stop_machine.c	stop_machine: make stop_machine safe and efficient to call early	2011-10-31 17:30:53 -07:00
sys_ni.c	Cross Memory Attach	2011-10-31 17:30:44 -07:00
sys.c
sysctl_binary.c
sysctl_check.c
sysctl.c	Merge branch 'akpm' (Andrew's incoming)	2011-10-31 17:46:07 -07:00
taskstats.c
test_kprobes.c
time.c
timeconst.pl
timer.c
tracepoint.c
tsacct.c
uid16.c
up.c
user_namespace.c
user-return-notifier.c
user.c
utsname_sysctl.c
utsname.c
wait.c
watchdog.c	watchdog: move watchdog_*_all_cpus under CONFIG_SYSCTL	2011-10-31 17:30:53 -07:00
workqueue_sched.h
workqueue.c