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    SubjectRe: [PATCH 1/2] Resource usage threshold notification addition to res_counter (v3)
    On Mon, 13 Jul 2009 17:16:20 -0700
    Vladislav Buzov <vbuzov@embeddedalley.com> wrote:

    > This patch updates the Resource Counter to add a configurable resource usage
    > threshold notification mechanism.
    >
    > Signed-off-by: Vladislav Buzov <vbuzov@embeddedalley.com>
    > Signed-off-by: Dan Malek <dan@embeddedalley.com>
    > ---
    > Documentation/cgroups/resource_counter.txt | 21 ++++++++-
    > include/linux/res_counter.h | 69 ++++++++++++++++++++++++++++
    > kernel/res_counter.c | 7 +++
    > 3 files changed, 95 insertions(+), 2 deletions(-)
    >
    > diff --git a/Documentation/cgroups/resource_counter.txt b/Documentation/cgroups/resource_counter.txt
    > index 95b24d7..1369dff 100644
    > --- a/Documentation/cgroups/resource_counter.txt
    > +++ b/Documentation/cgroups/resource_counter.txt
    > @@ -39,7 +39,20 @@ to work with it.
    > The failcnt stands for "failures counter". This is the number of
    > resource allocation attempts that failed.
    >
    > - c. spinlock_t lock
    > + e. unsigned long long threshold
    > +
    > + The resource usage threshold to notify the resouce controller. This is
    > + the minimal difference between the resource limit and current usage
    > + to fire a notification.
    > +
    > + f. void (*threshold_notifier)(struct res_counter *counter)
    > +
    > + The threshold notification callback installed by the resource
    > + controller. Called when the usage reaches or exceeds the threshold.
    > + Should be fast and not sleep because called when interrupts are
    > + disabled.
    > +

    This interface isn't very useful..hard to use..can't you just return the result as
    "exceeds threshold" to the callers ?

    If I was you, I'll add following state to res_counter

    enum {
    RES_BELOW_THRESH,
    RES_OVER_THRESH,
    } res_state;

    struct res_counter {
    .....
    enum res_state state;
    }

    Then, caller does
    example)
    prev_state = res->state;
    res_counter_charge(res....)
    if (prev_state != res->state)
    do_xxxxx..

    notifier under spinlock is not usual interface. And if this is "notifier",
    something generic, notifier_call_chain should be used rather than original
    one, IIUC.

    So, avoiding to use "callback" is a way to go, I think.

    Thanks,
    -Kame




    > + g. spinlock_t lock
    >
    > Protects changes of the above values.
    >
    > @@ -140,6 +153,7 @@ counter fields. They are recommended to adhere to the following rules:
    > usage usage_in_<unit_of_measurement>
    > max_usage max_usage_in_<unit_of_measurement>
    > limit limit_in_<unit_of_measurement>
    > + threshold notify_threshold_in_<unit_of_measurement>
    > failcnt failcnt
    > lock no file :)
    >
    > @@ -153,9 +167,12 @@ counter fields. They are recommended to adhere to the following rules:
    > usage prohibited
    > max_usage reset to usage
    > limit set the limit
    > + threshold set the threshold
    > failcnt reset to zero
    >
    > -
    > + d. Notification is enabled by installing the threshold notifier callback. It
    > + is up to the resouce controller to communicate the notification to user
    > + space tasks.
    >
    > 5. Usage example
    >
    > diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
    > index 511f42f..5ec98d7 100644
    > --- a/include/linux/res_counter.h
    > +++ b/include/linux/res_counter.h
    > @@ -9,6 +9,11 @@
    > *
    > * Author: Pavel Emelianov <xemul@openvz.org>
    > *
    > + * Resouce usage threshold notification update
    > + * Copyright 2009 CE Linux Forum and Embedded Alley Solutions, Inc.
    > + * Author: Dan Malek <dan@embeddedalley.com>
    > + * Author: Vladislav Buzov <vbuzov@embeddedalley.com>
    > + *
    > * See Documentation/cgroups/resource_counter.txt for more
    > * info about what this counter is.
    > */
    > @@ -35,6 +40,19 @@ struct res_counter {
    > */
    > unsigned long long limit;
    > /*
    > + * the resource usage threshold to notify the resouce controller. This
    > + * is the minimal difference between the resource limit and current
    > + * usage to fire a notification.
    > + */
    > + unsigned long long threshold;
    > + /*
    > + * the threshold notification callback installed by the resource
    > + * controller. Called when the usage reaches or exceeds the threshold.
    > + * Should be fast and not sleep because called when interrupts are
    > + * disabled.
    > + */
    > + void (*threshold_notifier)(struct res_counter *counter);
    > + /*
    > * the number of unsuccessful attempts to consume the resource
    > */
    > unsigned long long failcnt;
    > @@ -87,6 +105,7 @@ enum {
    > RES_MAX_USAGE,
    > RES_LIMIT,
    > RES_FAILCNT,
    > + RES_THRESHOLD,
    > };
    >
    > /*
    > @@ -132,6 +151,21 @@ static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
    > return false;
    > }
    >
    > +static inline bool res_counter_threshold_check_locked(struct res_counter *cnt)
    > +{
    > + if (cnt->usage + cnt->threshold < cnt->limit)
    > + return true;
    > +
    > + return false;
    > +}
    > +
    > +static inline void res_counter_threshold_notify_locked(struct res_counter *cnt)
    > +{
    > + if (!res_counter_threshold_check_locked(cnt) &&
    > + cnt->threshold_notifier)
    > + cnt->threshold_notifier(cnt);
    > +}
    > +
    > /*
    > * Helper function to detect if the cgroup is within it's limit or
    > * not. It's currently called from cgroup_rss_prepare()
    > @@ -147,6 +181,21 @@ static inline bool res_counter_check_under_limit(struct res_counter *cnt)
    > return ret;
    > }
    >
    > +/*
    > + * Helper function to detect if the cgroup usage is under it's threshold or
    > + * not.
    > + */
    > +static inline bool res_counter_check_under_threshold(struct res_counter *cnt)
    > +{
    > + bool ret;
    > + unsigned long flags;
    > +
    > + spin_lock_irqsave(&cnt->lock, flags);
    > + ret = res_counter_threshold_check_locked(cnt);
    > + spin_unlock_irqrestore(&cnt->lock, flags);
    > + return ret;
    > +}
    > +
    > static inline void res_counter_reset_max(struct res_counter *cnt)
    > {
    > unsigned long flags;
    > @@ -174,6 +223,26 @@ static inline int res_counter_set_limit(struct res_counter *cnt,
    > spin_lock_irqsave(&cnt->lock, flags);
    > if (cnt->usage <= limit) {
    > cnt->limit = limit;
    > + if (limit <= cnt->threshold)
    > + cnt->threshold = 0;
    > + else
    > + res_counter_threshold_notify_locked(cnt);
    > + ret = 0;
    > + }
    > + spin_unlock_irqrestore(&cnt->lock, flags);
    > + return ret;
    > +}
    > +
    > +static inline int res_counter_set_threshold(struct res_counter *cnt,
    > + unsigned long long threshold)
    > +{
    > + unsigned long flags;
    > + int ret = -EINVAL;
    > +
    > + spin_lock_irqsave(&cnt->lock, flags);
    > + if (cnt->limit > threshold) {
    > + cnt->threshold = threshold;
    > + res_counter_threshold_notify_locked(cnt);
    > ret = 0;
    > }
    > spin_unlock_irqrestore(&cnt->lock, flags);
    > diff --git a/kernel/res_counter.c b/kernel/res_counter.c
    > index e1338f0..9b36748 100644
    > --- a/kernel/res_counter.c
    > +++ b/kernel/res_counter.c
    > @@ -5,6 +5,10 @@
    > *
    > * Author: Pavel Emelianov <xemul@openvz.org>
    > *
    > + * Resouce usage threshold notification update
    > + * Copyright 2009 CE Linux Forum and Embedded Alley Solutions, Inc.
    > + * Author: Dan Malek <dan@embeddedalley.com>
    > + * Author: Vladislav Buzov <vbuzov@embeddedalley.com>
    > */
    >
    > #include <linux/types.h>
    > @@ -32,6 +36,7 @@ int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
    > counter->usage += val;
    > if (counter->usage > counter->max_usage)
    > counter->max_usage = counter->usage;
    > + res_counter_threshold_notify_locked(counter);
    > return 0;
    > }
    >
    > @@ -101,6 +106,8 @@ res_counter_member(struct res_counter *counter, int member)
    > return &counter->limit;
    > case RES_FAILCNT:
    > return &counter->failcnt;
    > + case RES_THRESHOLD:
    > + return &counter->threshold;
    > };
    >
    > BUG();
    > --
    > 1.5.6.3
    >
    >



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