linux-stable.git/kernel/sched/psi.c, branch v5.3

psi: get poll_work to run when calling poll syscall next time

2019-08-25T02:48:42+00:00

Only when calling the poll syscall the first time can user receive
POLLPRI correctly.  After that, user always fails to acquire the event
signal.

Reproduce case:
 1. Get the monitor code in Documentation/accounting/psi.txt
 2. Run it, and wait for the event triggered.
 3. Kill and restart the process.

The question is why we can end up with poll_scheduled = 1 but the work
not running (which would reset it to 0).  And the answer is because the
scheduling side sees group->poll_kworker under RCU protection and then
schedules it, but here we cancel the work and destroy the worker.  The
cancel needs to pair with resetting the poll_scheduled flag.

Link: http://lkml.kernel.org/r/1566357985-97781-1-git-send-email-joseph.qi@linux.alibaba.com
Signed-off-by: Jason Xing 
Signed-off-by: Joseph Qi 
Reviewed-by: Caspar Zhang 
Reviewed-by: Suren Baghdasaryan 
Acked-by: Johannes Weiner 
Cc: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

sched/psi: Do not require setsched permission from the trigger creator

2019-08-06T10:49:18+00:00

When a process creates a new trigger by writing into /proc/pressure/*
files, permissions to write such a file should be used to determine whether
the process is allowed to do so or not. Current implementation would also
require such a process to have setsched capability. Setting of psi trigger
thread's scheduling policy is an implementation detail and should not be
exposed to the user level. Remove the permission check by using _nocheck
version of the function.

Suggested-by: Nick Kralevich 
Signed-off-by: Suren Baghdasaryan 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: lizefan@huawei.com
Cc: mingo@redhat.com
Cc: akpm@linux-foundation.org
Cc: kernel-team@android.com
Cc: dennisszhou@gmail.com
Cc: dennis@kernel.org
Cc: hannes@cmpxchg.org
Cc: axboe@kernel.dk
Link: https://lkml.kernel.org/r/20190730013310.162367-1-surenb@google.com

sched/psi: Reduce psimon FIFO priority

2019-08-06T10:49:18+00:00

PSI defaults to a FIFO-99 thread, reduce this to FIFO-1.

FIFO-99 is the very highest priority available to SCHED_FIFO and
it not a suitable default; it would indicate the psi work is the
most important work on the machine.

Since Real-Time tasks will have pre-allocated memory and locked it in
place, Real-Time tasks do not care about PSI. All it needs is to be
above OTHER.

Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Johannes Weiner 
Tested-by: Suren Baghdasaryan 
Cc: Thomas Gleixner

kernel/sched/psi.c: expose pressure metrics on root cgroup

2019-05-15T02:52:48+00:00

Pressure metrics are already recorded and exposed in procfs for the
entire system, but any tool which monitors cgroup pressure has to
special case the root cgroup to read from procfs.  This patch exposes
the already recorded pressure metrics on the root cgroup.

Link: http://lkml.kernel.org/r/20190510174938.3361741-1-dschatzberg@fb.com
Signed-off-by: Dan Schatzberg 
Acked-by: Johannes Weiner 
Cc: Tejun Heo 
Cc: Li Zefan 
Cc: Ingo Molnar 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

psi: introduce psi monitor

2019-05-15T02:52:48+00:00

Psi monitor aims to provide a low-latency short-term pressure detection
mechanism configurable by users.  It allows users to monitor psi metrics
growth and trigger events whenever a metric raises above user-defined
threshold within user-defined time window.

Time window and threshold are both expressed in usecs.  Multiple psi
resources with different thresholds and window sizes can be monitored
concurrently.

Psi monitors activate when system enters stall state for the monitored
psi metric and deactivate upon exit from the stall state.  While system
is in the stall state psi signal growth is monitored at a rate of 10
times per tracking window.  Min window size is 500ms, therefore the min
monitoring interval is 50ms.  Max window size is 10s with monitoring
interval of 1s.

When activated psi monitor stays active for at least the duration of one
tracking window to avoid repeated activations/deactivations when psi
signal is bouncing.

Notifications to the users are rate-limited to one per tracking window.

Link: http://lkml.kernel.org/r/20190319235619.260832-8-surenb@google.com
Signed-off-by: Suren Baghdasaryan 
Signed-off-by: Johannes Weiner 
Cc: Dennis Zhou 
Cc: Ingo Molnar 
Cc: Jens Axboe 
Cc: Li Zefan 
Cc: Peter Zijlstra 
Cc: Tejun Heo 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

psi: track changed states

2019-05-15T02:52:48+00:00

Introduce changed_states parameter into collect_percpu_times to track
the states changed since the last update.

This will be needed to detect whether polled states activated in the
monitor patch.

Link: http://lkml.kernel.org/r/20190319235619.260832-6-surenb@google.com
Signed-off-by: Suren Baghdasaryan 
Acked-by: Johannes Weiner 
Cc: Dennis Zhou 
Cc: Ingo Molnar 
Cc: Jens Axboe 
Cc: Li Zefan 
Cc: Peter Zijlstra 
Cc: Tejun Heo 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

psi: split update_stats into parts

2019-05-15T02:52:47+00:00

Split update_stats into collect_percpu_times and update_averages for
collect_percpu_times to be reused later inside psi monitor.

Link: http://lkml.kernel.org/r/20190319235619.260832-5-surenb@google.com
Signed-off-by: Suren Baghdasaryan 
Acked-by: Johannes Weiner 
Cc: Dennis Zhou 
Cc: Ingo Molnar 
Cc: Jens Axboe 
Cc: Li Zefan 
Cc: Peter Zijlstra 
Cc: Tejun Heo 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

psi: rename psi fields in preparation for psi trigger addition

2019-05-15T02:52:47+00:00

Rename psi_group structure member fields used for calculating psi totals
and averages for clear distinction between them and for trigger-related
fields that will be added by "psi: introduce psi monitor".

[surenb@google.com: v6]
  Link: http://lkml.kernel.org/r/20190319235619.260832-4-surenb@google.com
Link: http://lkml.kernel.org/r/20190124211518.244221-5-surenb@google.com
Signed-off-by: Suren Baghdasaryan 
Acked-by: Johannes Weiner 
Cc: Dennis Zhou 
Cc: Ingo Molnar 
Cc: Jens Axboe 
Cc: Li Zefan 
Cc: Peter Zijlstra 
Cc: Tejun Heo 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

psi: make psi_enable static

2019-05-15T02:52:47+00:00

psi_enable is not used outside of psi.c, make it static.

Link: http://lkml.kernel.org/r/20190319235619.260832-3-surenb@google.com
Signed-off-by: Suren Baghdasaryan 
Suggested-by: Andrew Morton 
Acked-by: Johannes Weiner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

psi: introduce state_mask to represent stalled psi states

2019-05-15T02:52:47+00:00

Patch series "psi: pressure stall monitors", v6.

This is a respin of:
  https://lwn.net/ml/linux-kernel/20190308184311.144521-1-surenb%40google.com/

Android is adopting psi to detect and remedy memory pressure that
results in stuttering and decreased responsiveness on mobile devices.

Psi gives us the stall information, but because we're dealing with
latencies in the millisecond range, periodically reading the pressure
files to detect stalls in a timely fashion is not feasible.  Psi also
doesn't aggregate its averages at a high-enough frequency right now.

This patch series extends the psi interface such that users can
configure sensitive latency thresholds and use poll() and friends to be
notified when these are breached.

As high-frequency aggregation is costly, it implements an aggregation
method that is optimized for fast, short-interval averaging, and makes
the aggregation frequency adaptive, such that high-frequency updates
only happen while monitored stall events are actively occurring.

With these patches applied, Android can monitor for, and ward off,
mounting memory shortages before they cause problems for the user.  For
example, using memory stall monitors in userspace low memory killer
daemon (lmkd) we can detect mounting pressure and kill less important
processes before device becomes visibly sluggish.  In our memory stress
testing psi memory monitors produce roughly 10x less false positives
compared to vmpressure signals.  Having ability to specify multiple
triggers for the same psi metric allows other parts of Android framework
to monitor memory state of the device and act accordingly.

The new interface is straight-forward.  The user opens one of the
pressure files for writing and writes a trigger description into the
file descriptor that defines the stall state - some or full, and the
maximum stall time over a given window of time.  E.g.:

        /* Signal when stall time exceeds 100ms of a 1s window */
        char trigger[] = "full 100000 1000000"
        fd = open("/proc/pressure/memory")
        write(fd, trigger, sizeof(trigger))
        while (poll() >= 0) {
                ...
        };
        close(fd);

When the monitored stall state is entered, psi adapts its aggregation
frequency according to what the configured time window requires in order
to emit event signals in a timely fashion.  Once the stalling subsides,
aggregation reverts back to normal.

The trigger is associated with the open file descriptor.  To stop
monitoring, the user only needs to close the file descriptor and the
trigger is discarded.

Patches 1-6 prepare the psi code for polling support.  Patch 7
implements the adaptive polling logic, the pressure growth detection
optimized for short intervals, and hooks up write() and poll() on the
pressure files.

The patches were developed in collaboration with Johannes Weiner.

This patch (of 7):

The psi monitoring patches will need to determine the same states as
record_times().  To avoid calculating them twice, maintain a state mask
that can be consulted cheaply.  Do this in a separate patch to keep the
churn in the main feature patch at a minimum.

This adds 4-byte state_mask member into psi_group_cpu struct which
results in its first cacheline-aligned part becoming 52 bytes long.  Add
explicit values to enumeration element counters that affect
psi_group_cpu struct size.

Link: http://lkml.kernel.org/r/20190124211518.244221-4-surenb@google.com
Signed-off-by: Suren Baghdasaryan 
Acked-by: Johannes Weiner 
Cc: Dennis Zhou 
Cc: Ingo Molnar 
Cc: Jens Axboe 
Cc: Li Zefan 
Cc: Peter Zijlstra 
Cc: Tejun Heo 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds