linux.git/Documentation/filesystems/proc.txt, branch v3.0.82

rcu: Use softirq to address performance regression

2011-06-14T22:25:39+00:00

Commit a26ac2455ffcf3(rcu: move TREE_RCU from softirq to kthread)
introduced performance regression. In an AIM7 test, this commit degraded
performance by about 40%.

The commit runs rcu callbacks in a kthread instead of softirq. We observed
high rate of context switch which is caused by this. Out test system has
64 CPUs and HZ is 1000, so we saw more than 64k context switch per second
which is caused by RCU's per-CPU kthread.  A trace showed that most of
the time the RCU per-CPU kthread doesn't actually handle any callbacks,
but instead just does a very small amount of work handling grace periods.
This means that RCU's per-CPU kthreads are making the scheduler do quite
a bit of work in order to allow a very small amount of RCU-related
processing to be done.

Alex Shi's analysis determined that this slowdown is due to lock
contention within the scheduler.  Unfortunately, as Peter Zijlstra points
out, the scheduler's real-time semantics require global action, which
means that this contention is inherent in real-time scheduling.  (Yes,
perhaps someone will come up with a workaround -- otherwise, -rt is not
going to do well on large SMP systems -- but this patch will work around
this issue in the meantime.  And "the meantime" might well be forever.)

This patch therefore re-introduces softirq processing to RCU, but only
for core RCU work.  RCU callbacks are still executed in kthread context,
so that only a small amount of RCU work runs in softirq context in the
common case.  This should minimize ksoftirqd execution, allowing us to
skip boosting of ksoftirqd for CONFIG_RCU_BOOST=y kernels.

Signed-off-by: Shaohua Li 
Tested-by: "Alex,Shi" 
Signed-off-by: Paul E. McKenney

bitmap, irq: add smp_affinity_list interface to /proc/irq

2011-05-25T15:39:45+00:00

Manually adjusting the smp_affinity for IRQ's becomes unwieldy when the
cpu count is large.

Setting smp affinity to cpus 256 to 263 would be:

	echo 000000ff,00000000,00000000,00000000,00000000,00000000,00000000,00000000 > smp_affinity

instead of:

	echo 256-263 > smp_affinity_list

Think about what it looks like for cpus around say, 4088 to 4095.

We already have many alternate "list" interfaces:

/sys/devices/system/cpu/cpuX/indexY/shared_cpu_list
/sys/devices/system/cpu/cpuX/topology/thread_siblings_list
/sys/devices/system/cpu/cpuX/topology/core_siblings_list
/sys/devices/system/node/nodeX/cpulist
/sys/devices/pci***/***/local_cpulist

Add a companion interface, smp_affinity_list to use cpu lists instead of
cpu maps.  This conforms to other companion interfaces where both a map
and a list interface exists.

This required adding a bitmap_parselist_user() function in a manner
similar to the bitmap_parse_user() function.

[akpm@linux-foundation.org: make __bitmap_parselist() static]
Signed-off-by: Mike Travis 
Cc: Thomas Gleixner 
Cc: Jack Steiner 
Cc: Lee Schermerhorn 
Cc: Andy Shevchenko 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

rcu: move TREE_RCU from softirq to kthread

2011-05-06T06:16:54+00:00

If RCU priority boosting is to be meaningful, callback invocation must
be boosted in addition to preempted RCU readers.  Otherwise, in presence
of CPU real-time threads, the grace period ends, but the callbacks don't
get invoked.  If the callbacks don't get invoked, the associated memory
doesn't get freed, so the system is still subject to OOM.

But it is not reasonable to priority-boost RCU_SOFTIRQ, so this commit
moves the callback invocations to a kthread, which can be boosted easily.

Also add comments and properly synchronized all accesses to
rcu_cpu_kthread_task, as suggested by Lai Jiangshan.

Signed-off-by: Paul E. McKenney 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Josh Triplett

Fix common misspellings

2011-03-31T14:26:23+00:00

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi

oom: allow a non-CAP_SYS_RESOURCE proces to oom_score_adj down

2011-01-14T01:32:35+00:00

We'd like to be able to oom_score_adj a process up/down as it
enters/leaves the foreground.  Currently, it is not possible to oom_adj
down without CAP_SYS_RESOURCE.  This patch allows a task to decrease its
oom_score_adj back to the value that a CAP_SYS_RESOURCE thread set it to
or its inherited value at fork.  Assuming the thread that has forked it
has oom_score_adj of 0, each process could decrease it back from 0 upon
activation unless a CAP_SYS_RESOURCE thread elevated it to something
higher.

Alternative considered:

* a setuid binary
* a daemon with CAP_SYS_RESOURCE

Since you don't wan't all processes to be able to reduce their oom_adj, a
setuid or daemon implementation would be complex.  The alternatives also
have much higher overhead.

This patch updated from original patch based on feedback from David
Rientjes.

Signed-off-by: Mandeep Singh Baines 
Acked-by: David Rientjes 
Cc: KAMEZAWA Hiroyuki 
Cc: KOSAKI Motohiro 
Cc: Rik van Riel 
Cc: Ying Han 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: smaps: export mlock information

2011-01-14T01:32:33+00:00

Currently there is no way to find whether a process has locked its pages
in memory or not.  And which of the memory regions are locked in memory.

Add a new field "Locked" to export this information via the smaps file.

Signed-off-by: Nikanth Karthikesan 
Acked-by: Balbir Singh 
Acked-by: Wu Fengguang 
Cc: Matt Mackall 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

console: add /proc/consoles

2010-11-16T20:50:17+00:00

It allows users to see what consoles are currently known to the system
and with what flags.

It is based on Werner's patch, the part about traversing fds was
removed, the code was moved to kernel/printk.c, where consoles are
handled and it makes more sense to me.

Signed-off-by: Jiri Slaby  [cleanups]
Signed-off-by: "Dr. Werner Fink" 
Cc: Al Viro 
Cc: Greg Kroah-Hartman 
Signed-off-by: Greg Kroah-Hartman

/proc/pid/pagemap: document in Documentation/filesystems/proc.txt

2010-10-28T01:03:13+00:00

Document /proc/pid/pagemap in Documentation/filesystems/proc.txt

Signed-off-by: Nikanth Karthikesan 
Cc: Richard Guenther 
Cc: Balbir Singh 
Cc: KOSAKI Motohiro 
Acked-by: Matt Mackall 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

/proc/pid/smaps: export amount of anonymous memory in a mapping

2010-10-28T01:03:13+00:00

Export the number of anonymous pages in a mapping via smaps.

Even the private pages in a mapping backed by a file, would be marked as
anonymous, when they are modified. Export this information to user-space via
smaps.

Exporting this count will help gdb to make a better decision on which
areas need to be dumped in its coredump; and should be useful to others
studying the memory usage of a process.

Signed-off-by: Nikanth Karthikesan 
Acked-by: Hugh Dickins 
Reviewed-by: KOSAKI Motohiro 
Cc: Matt Mackall 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Documentation/filesystems/proc.txt: improve smaps field documentation

2010-10-26T23:52:05+00:00

Signed-off-by: Matt Mackall 
Cc: Nikanth Karthikesan 
Cc: Balbir Singh 
Cc: Wu Fengguang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds