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    Subject[RFI] Help Resource Counters scale better

    Enhancement: For scalability move the resource counter to a percpu counter

    From: Balbir Singh <balbir@linux.vnet.ibm.com>

    This patch changes the usage field of a resource counter to a percpu
    counter. The counter is incremented with local irq disabled. The other
    fields are still protected by the spin lock for write.

    This patch adds a fuzziness factor to hard limit, since the value we read
    could be off the original value (by batch value), this can be fixed
    by adding a strict/non-strict functionality check. The intention is
    to turn of strict checking for root (since we can't set limits on
    it anyway).

    I tested this patch on my x86_64 box with a regular test for hard
    limits and a page fault program.

    This is an early RFI on the design and changes for resource counter
    functionality to help it scale better.

    Direct uses of mem->res.usage in memcontrol.c have been converted
    to the standard resource counters interface.

    Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
    ---

    include/linux/res_counter.h | 41 ++++++++++++++++++++++++-----------------
    kernel/res_counter.c | 31 +++++++++++++++++--------------
    mm/memcontrol.c | 6 +++---
    3 files changed, 44 insertions(+), 34 deletions(-)


    diff --git a/include/linux/res_counter.h b/include/linux/res_counter.h
    index 731af71..0f9ee03 100644
    --- a/include/linux/res_counter.h
    +++ b/include/linux/res_counter.h
    @@ -14,6 +14,7 @@
    */

    #include <linux/cgroup.h>
    +#include <linux/percpu_counter.h>

    /*
    * The core object. the cgroup that wishes to account for some
    @@ -23,10 +24,6 @@

    struct res_counter {
    /*
    - * the current resource consumption level
    - */
    - unsigned long long usage;
    - /*
    * the maximal value of the usage from the counter creation
    */
    unsigned long long max_usage;
    @@ -48,6 +45,11 @@ struct res_counter {
    */
    spinlock_t lock;
    /*
    + * the current resource consumption level
    + */
    + struct percpu_counter usage;
    + unsigned long long tmp_usage; /* Used by res_counter_member */
    + /*
    * Parent counter, used for hierarchial resource accounting
    */
    struct res_counter *parent;
    @@ -133,7 +135,8 @@ void res_counter_uncharge(struct res_counter *counter, unsigned long val,

    static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
    {
    - if (cnt->usage < cnt->limit)
    + unsigned long long usage = percpu_counter_read_positive(&cnt->usage);
    + if (usage < cnt->limit)
    return true;

    return false;
    @@ -141,7 +144,8 @@ static inline bool res_counter_limit_check_locked(struct res_counter *cnt)

    static inline bool res_counter_soft_limit_check_locked(struct res_counter *cnt)
    {
    - if (cnt->usage < cnt->soft_limit)
    + unsigned long long usage = percpu_counter_read_positive(&cnt->usage);
    + if (usage < cnt->soft_limit)
    return true;

    return false;
    @@ -157,15 +161,16 @@ static inline bool res_counter_soft_limit_check_locked(struct res_counter *cnt)
    static inline unsigned long long
    res_counter_soft_limit_excess(struct res_counter *cnt)
    {
    - unsigned long long excess;
    + unsigned long long excess, usage;
    unsigned long flags;

    - spin_lock_irqsave(&cnt->lock, flags);
    - if (cnt->usage <= cnt->soft_limit)
    + local_irq_save(flags);
    + usage = percpu_counter_read_positive(&cnt->usage);
    + if (usage <= cnt->soft_limit)
    excess = 0;
    else
    - excess = cnt->usage - cnt->soft_limit;
    - spin_unlock_irqrestore(&cnt->lock, flags);
    + excess = usage - cnt->soft_limit;
    + local_irq_restore(flags);
    return excess;
    }

    @@ -178,9 +183,9 @@ static inline bool res_counter_check_under_limit(struct res_counter *cnt)
    bool ret;
    unsigned long flags;

    - spin_lock_irqsave(&cnt->lock, flags);
    + local_irq_save(flags);
    ret = res_counter_limit_check_locked(cnt);
    - spin_unlock_irqrestore(&cnt->lock, flags);
    + local_irq_restore(flags);
    return ret;
    }

    @@ -189,18 +194,19 @@ static inline bool res_counter_check_under_soft_limit(struct res_counter *cnt)
    bool ret;
    unsigned long flags;

    - spin_lock_irqsave(&cnt->lock, flags);
    + local_irq_save(flags);
    ret = res_counter_soft_limit_check_locked(cnt);
    - spin_unlock_irqrestore(&cnt->lock, flags);
    + local_irq_restore(flags);
    return ret;
    }

    static inline void res_counter_reset_max(struct res_counter *cnt)
    {
    unsigned long flags;
    + unsigned long long usage = percpu_counter_read_positive(&cnt->usage);

    spin_lock_irqsave(&cnt->lock, flags);
    - cnt->max_usage = cnt->usage;
    + cnt->max_usage = usage;
    spin_unlock_irqrestore(&cnt->lock, flags);
    }

    @@ -217,10 +223,11 @@ static inline int res_counter_set_limit(struct res_counter *cnt,
    unsigned long long limit)
    {
    unsigned long flags;
    + unsigned long long usage = percpu_counter_read_positive(&cnt->usage);
    int ret = -EBUSY;

    spin_lock_irqsave(&cnt->lock, flags);
    - if (cnt->usage <= limit) {
    + if (usage <= limit) {
    cnt->limit = limit;
    ret = 0;
    }
    diff --git a/kernel/res_counter.c b/kernel/res_counter.c
    index 88faec2..730a60d 100644
    --- a/kernel/res_counter.c
    +++ b/kernel/res_counter.c
    @@ -18,6 +18,7 @@
    void res_counter_init(struct res_counter *counter, struct res_counter *parent)
    {
    spin_lock_init(&counter->lock);
    + percpu_counter_init(&counter->usage, 0);
    counter->limit = RESOURCE_MAX;
    counter->soft_limit = RESOURCE_MAX;
    counter->parent = parent;
    @@ -25,14 +26,17 @@ void res_counter_init(struct res_counter *counter, struct res_counter *parent)

    int res_counter_charge_locked(struct res_counter *counter, unsigned long val)
    {
    - if (counter->usage + val > counter->limit) {
    + unsigned long long usage;
    +
    + usage = percpu_counter_read_positive(&counter->usage);
    + if (usage + val > counter->limit) {
    counter->failcnt++;
    return -ENOMEM;
    }

    - counter->usage += val;
    - if (counter->usage > counter->max_usage)
    - counter->max_usage = counter->usage;
    + __percpu_counter_add(&counter->usage, val, nr_cpu_ids * PAGE_SIZE);
    + if (usage + val > counter->max_usage)
    + counter->max_usage = (usage + val);
    return 0;
    }

    @@ -49,7 +53,6 @@ int res_counter_charge(struct res_counter *counter, unsigned long val,
    *soft_limit_fail_at = NULL;
    local_irq_save(flags);
    for (c = counter; c != NULL; c = c->parent) {
    - spin_lock(&c->lock);
    ret = res_counter_charge_locked(c, val);
    /*
    * With soft limits, we return the highest ancestor
    @@ -58,7 +61,6 @@ int res_counter_charge(struct res_counter *counter, unsigned long val,
    if (soft_limit_fail_at &&
    !res_counter_soft_limit_check_locked(c))
    *soft_limit_fail_at = c;
    - spin_unlock(&c->lock);
    if (ret < 0) {
    *limit_fail_at = c;
    goto undo;
    @@ -68,9 +70,7 @@ int res_counter_charge(struct res_counter *counter, unsigned long val,
    goto done;
    undo:
    for (u = counter; u != c; u = u->parent) {
    - spin_lock(&u->lock);
    res_counter_uncharge_locked(u, val);
    - spin_unlock(&u->lock);
    }
    done:
    local_irq_restore(flags);
    @@ -79,10 +79,13 @@ done:

    void res_counter_uncharge_locked(struct res_counter *counter, unsigned long val)
    {
    - if (WARN_ON(counter->usage < val))
    - val = counter->usage;
    + unsigned long long usage;
    +
    + usage = percpu_counter_read_positive(&counter->usage);
    + if (WARN_ON((usage + nr_cpu_ids * PAGE_SIZE) < val))
    + val = usage;

    - counter->usage -= val;
    + percpu_counter_sub(&counter->usage, val);
    }

    void res_counter_uncharge(struct res_counter *counter, unsigned long val,
    @@ -93,12 +96,10 @@ void res_counter_uncharge(struct res_counter *counter, unsigned long val,

    local_irq_save(flags);
    for (c = counter; c != NULL; c = c->parent) {
    - spin_lock(&c->lock);
    if (was_soft_limit_excess)
    *was_soft_limit_excess =
    !res_counter_soft_limit_check_locked(c);
    res_counter_uncharge_locked(c, val);
    - spin_unlock(&c->lock);
    }
    local_irq_restore(flags);
    }
    @@ -109,7 +110,9 @@ res_counter_member(struct res_counter *counter, int member)
    {
    switch (member) {
    case RES_USAGE:
    - return &counter->usage;
    + counter->tmp_usage =
    + percpu_counter_read_positive(&counter->usage);
    + return &counter->tmp_usage;
    case RES_MAX_USAGE:
    return &counter->max_usage;
    case RES_LIMIT:
    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index 362b711..f138b6c 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -2342,7 +2342,7 @@ static int mem_cgroup_force_empty(struct mem_cgroup *mem, bool free_all)
    if (free_all)
    goto try_to_free;
    move_account:
    - while (mem->res.usage > 0) {
    + while (res_counter_read_u64(&mem->res, RES_USAGE) > 0) {
    ret = -EBUSY;
    if (cgroup_task_count(cgrp) || !list_empty(&cgrp->children))
    goto out;
    @@ -2385,7 +2385,7 @@ try_to_free:
    lru_add_drain_all();
    /* try to free all pages in this cgroup */
    shrink = 1;
    - while (nr_retries && mem->res.usage > 0) {
    + while (nr_retries && res_counter_read_u64(&mem->res, RES_USAGE) > 0) {
    int progress;

    if (signal_pending(current)) {
    @@ -2403,7 +2403,7 @@ try_to_free:
    }
    lru_add_drain();
    /* try move_account...there may be some *locked* pages. */
    - if (mem->res.usage)
    + if (res_counter_read_u64(&mem->res, RES_USAGE))
    goto move_account;
    ret = 0;
    goto out;
    --
    Balbir


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