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SubjectRe: [RFC][PATCH 1/2] memcg: oom notifier
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On Mon, Mar 8, 2010 at 9:25 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
> Considering containers or other resource management softwares in userland,
> event notification of OOM in memcg should be implemented.
> Now, memcg has "threshold" notifier which uses eventfd, we can make
> use of it for oom notification.
>
> This patch adds oom notification eventfd callback for memcg. The usage
> is very similar to threshold notifier, but control file is
> memory.oom_control and no arguments other than eventfd is required.
>
>        % cgroup_event_notifier /cgroup/A/memory.oom_control dummy
>        (About cgroup_event_notifier, see Documentation/cgroup/)

Nice idea!

But I don't think that sharing mem_cgroup_(un)register_event()
with thresholds is a good idea. There are too many
"if (type != _OOM_TYPE)". Probably, it's cleaner to create separate
register/unregister for oom events, since oom event is quite different
from threshold. We, also, don't need RCU for oom events. It's not
a critical path.

> TODO:
>  - add a knob to disable oom-kill under a memcg.
>  - add read/write function to oom_control
>
> Changelog: 20100304
>  - renewed implemnation.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  Documentation/cgroups/memory.txt |   20 ++++-
>  mm/memcontrol.c                  |  155 ++++++++++++++++++++++++++++-----------
>  2 files changed, 131 insertions(+), 44 deletions(-)
>
> Index: mmotm-2.6.33-Mar5/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.33-Mar5.orig/mm/memcontrol.c
> +++ mmotm-2.6.33-Mar5/mm/memcontrol.c
> @@ -159,6 +159,7 @@ struct mem_cgroup_threshold_ary {
>  };
>
>  static void mem_cgroup_threshold(struct mem_cgroup *mem);
> +static void mem_cgroup_oom_notify(struct mem_cgroup *mem);
>
>  /*
>  * The memory controller data structure. The memory controller controls both
> @@ -220,6 +221,9 @@ struct mem_cgroup {
>        /* thresholds for mem+swap usage. RCU-protected */
>        struct mem_cgroup_threshold_ary *memsw_thresholds;
>
> +       /* For oom notifier event fd */
> +       struct mem_cgroup_threshold_ary *oom_notify;
> +
>        /*
>         * Should we move charges of a task when a task is moved into this
>         * mem_cgroup ? And what type of charges should we move ?
> @@ -282,9 +286,12 @@ enum charge_type {
>  /* for encoding cft->private value on file */
>  #define _MEM                   (0)
>  #define _MEMSWAP               (1)
> +#define _OOM_TYPE              (2)
>  #define MEMFILE_PRIVATE(x, val)        (((x) << 16) | (val))
>  #define MEMFILE_TYPE(val)      (((val) >> 16) & 0xffff)
>  #define MEMFILE_ATTR(val)      ((val) & 0xffff)
> +/* Used for OOM nofiier */
> +#define OOM_CONTROL            (0)
>
>  /*
>  * Reclaim flags for mem_cgroup_hierarchical_reclaim
> @@ -1313,9 +1320,10 @@ bool mem_cgroup_handle_oom(struct mem_cg
>                prepare_to_wait(&memcg_oom_waitq, &wait, TASK_KILLABLE);
>        mutex_unlock(&memcg_oom_mutex);
>
> -       if (locked)
> +       if (locked) {
> +               mem_cgroup_oom_notify(mem);
>                mem_cgroup_out_of_memory(mem, mask);
> -       else {
> +       } else {
>                schedule();
>                finish_wait(&memcg_oom_waitq, &wait);
>        }
> @@ -3363,33 +3371,65 @@ static int compare_thresholds(const void
>        return _a->threshold - _b->threshold;
>  }
>
> +static int mem_cgroup_oom_notify_cb(struct mem_cgroup *mem, void *data)
> +{
> +       struct mem_cgroup_threshold_ary *x;
> +       int i;
> +
> +       rcu_read_lock();
> +       x = rcu_dereference(mem->oom_notify);
> +       for (i = 0; x && i < x->size; i++)
> +               eventfd_signal(x->entries[i].eventfd, 1);
> +       rcu_read_unlock();
> +       return 0;
> +}
> +
> +static void mem_cgroup_oom_notify(struct mem_cgroup *mem)
> +{
> +       mem_cgroup_walk_tree(mem, NULL, mem_cgroup_oom_notify_cb);
> +}
> +
>  static int mem_cgroup_register_event(struct cgroup *cgrp, struct cftype *cft,
>                struct eventfd_ctx *eventfd, const char *args)
>  {
>        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
>        struct mem_cgroup_threshold_ary *thresholds, *thresholds_new;
>        int type = MEMFILE_TYPE(cft->private);
> -       u64 threshold, usage;
> +       u64 threshold;
> +       u64 usage = 0;
>        int size;
>        int i, ret;
>
> -       ret = res_counter_memparse_write_strategy(args, &threshold);
> -       if (ret)
> -               return ret;
> +       if (type != _OOM_TYPE) {
> +               ret = res_counter_memparse_write_strategy(args, &threshold);
> +               if (ret)
> +                       return ret;
> +       } else if (mem_cgroup_is_root(memcg)) /* root cgroup ? */
> +               return -ENOTSUPP;
>
>        mutex_lock(&memcg->thresholds_lock);
> -       if (type == _MEM)
> +       /* For waiting OOM notify, "-1" is passed */
> +
> +       switch (type) {
> +       case _MEM:
>                thresholds = memcg->thresholds;
> -       else if (type == _MEMSWAP)
> +               break;
> +       case _MEMSWAP:
>                thresholds = memcg->memsw_thresholds;
> -       else
> +               break;
> +       case _OOM_TYPE:
> +               thresholds = memcg->oom_notify;
> +               break;
> +       default:
>                BUG();
> +       }
>
> -       usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
> -
> -       /* Check if a threshold crossed before adding a new one */
> -       if (thresholds)
> -               __mem_cgroup_threshold(memcg, type == _MEMSWAP);
> +       if (type != _OOM_TYPE) {
> +               usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
> +               /* Check if a threshold crossed before adding a new one */
> +               if (thresholds)
> +                       __mem_cgroup_threshold(memcg, type == _MEMSWAP);
> +       }
>
>        if (thresholds)
>                size = thresholds->size + 1;
> @@ -3416,27 +3456,34 @@ static int mem_cgroup_register_event(str
>        thresholds_new->entries[size - 1].threshold = threshold;
>
>        /* Sort thresholds. Registering of new threshold isn't time-critical */
> -       sort(thresholds_new->entries, size,
> +       if (type != _OOM_TYPE) {
> +               sort(thresholds_new->entries, size,
>                        sizeof(struct mem_cgroup_threshold),
>                        compare_thresholds, NULL);
> -
> -       /* Find current threshold */
> -       atomic_set(&thresholds_new->current_threshold, -1);
> -       for (i = 0; i < size; i++) {
> -               if (thresholds_new->entries[i].threshold < usage) {
> -                       /*
> -                        * thresholds_new->current_threshold will not be used
> -                        * until rcu_assign_pointer(), so it's safe to increment
> -                        * it here.
> -                        */
> -                       atomic_inc(&thresholds_new->current_threshold);
> +               /* Find current threshold */
> +               atomic_set(&thresholds_new->current_threshold, -1);
> +               for (i = 0; i < size; i++) {
> +                       if (thresholds_new->entries[i].threshold < usage) {
> +                               /*
> +                                * thresholds_new->current_threshold will not
> +                                * be used until rcu_assign_pointer(), so it's
> +                                * safe to increment it here.
> +                                */
> +                               atomic_inc(&thresholds_new->current_threshold);
> +                       }
>                }
>        }
> -
> -       if (type == _MEM)
> +       switch (type) {
> +       case _MEM:
>                rcu_assign_pointer(memcg->thresholds, thresholds_new);
> -       else
> +               break;
> +       case _MEMSWAP:
>                rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
> +               break;
> +       case _OOM_TYPE:
> +               rcu_assign_pointer(memcg->oom_notify, thresholds_new);
> +               break;
> +       }
>
>        /* To be sure that nobody uses thresholds before freeing it */
>        synchronize_rcu();
> @@ -3454,17 +3501,25 @@ static int mem_cgroup_unregister_event(s
>        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
>        struct mem_cgroup_threshold_ary *thresholds, *thresholds_new;
>        int type = MEMFILE_TYPE(cft->private);
> -       u64 usage;
> +       u64 usage = 0;
>        int size = 0;
>        int i, j, ret;
>
>        mutex_lock(&memcg->thresholds_lock);
> -       if (type == _MEM)
> +       /* check eventfd is for OOM check or not */
> +       switch (type) {
> +       case _MEM:
>                thresholds = memcg->thresholds;
> -       else if (type == _MEMSWAP)
> +               break;
> +       case _MEMSWAP:
>                thresholds = memcg->memsw_thresholds;
> -       else
> +               break;
> +       case _OOM_TYPE:
> +               thresholds = memcg->oom_notify;
> +               break;
> +       default:
>                BUG();
> +       }
>
>        /*
>         * Something went wrong if we trying to unregister a threshold
> @@ -3472,11 +3527,11 @@ static int mem_cgroup_unregister_event(s
>         */
>        BUG_ON(!thresholds);
>
> -       usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
> -
> -       /* Check if a threshold crossed before removing */
> -       __mem_cgroup_threshold(memcg, type == _MEMSWAP);
> -
> +       if (type != _OOM_TYPE) {
> +               usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
> +               /* Check if a threshold crossed before removing */
> +               __mem_cgroup_threshold(memcg, type == _MEMSWAP);
> +       }
>        /* Calculate new number of threshold */
>        for (i = 0; i < thresholds->size; i++) {
>                if (thresholds->entries[i].eventfd != eventfd)
> @@ -3500,13 +3555,15 @@ static int mem_cgroup_unregister_event(s
>        thresholds_new->size = size;
>
>        /* Copy thresholds and find current threshold */
> -       atomic_set(&thresholds_new->current_threshold, -1);
> +       if (type != _OOM_TYPE)
> +               atomic_set(&thresholds_new->current_threshold, -1);
>        for (i = 0, j = 0; i < thresholds->size; i++) {
>                if (thresholds->entries[i].eventfd == eventfd)
>                        continue;
>
>                thresholds_new->entries[j] = thresholds->entries[i];
> -               if (thresholds_new->entries[j].threshold < usage) {
> +               if (type != _OOM_TYPE &&
> +                       thresholds_new->entries[j].threshold < usage) {
>                        /*
>                         * thresholds_new->current_threshold will not be used
>                         * until rcu_assign_pointer(), so it's safe to increment
> @@ -3518,11 +3575,17 @@ static int mem_cgroup_unregister_event(s
>        }
>
>  assign:
> -       if (type == _MEM)
> +       switch (type) {
> +       case _MEM:
>                rcu_assign_pointer(memcg->thresholds, thresholds_new);
> -       else
> +               break;
> +       case _MEMSWAP:
>                rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
> -
> +               break;
> +       case _OOM_TYPE:
> +               rcu_assign_pointer(memcg->oom_notify, thresholds_new);
> +               break;
> +       }
>        /* To be sure that nobody uses thresholds before freeing it */
>        synchronize_rcu();
>
> @@ -3588,6 +3651,12 @@ static struct cftype mem_cgroup_files[]
>                .read_u64 = mem_cgroup_move_charge_read,
>                .write_u64 = mem_cgroup_move_charge_write,
>        },
> +       {
> +               .name = "oom_control",
> +               .register_event = mem_cgroup_register_event,
> +               .unregister_event = mem_cgroup_unregister_event,
> +               .private = MEMFILE_PRIVATE(_OOM_TYPE, OOM_CONTROL),
> +       },
>  };
>
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
> Index: mmotm-2.6.33-Mar5/Documentation/cgroups/memory.txt
> ===================================================================
> --- mmotm-2.6.33-Mar5.orig/Documentation/cgroups/memory.txt
> +++ mmotm-2.6.33-Mar5/Documentation/cgroups/memory.txt
> @@ -184,6 +184,9 @@ limits on the root cgroup.
>
>  Note2: When panic_on_oom is set to "2", the whole system will panic.
>
> +When oom event notifier is registered, event will be delivered.
> +(See oom_control section)
> +
>  2. Locking
>
>  The memory controller uses the following hierarchy
> @@ -486,7 +489,22 @@ threshold in any direction.
>
>  It's applicable for root and non-root cgroup.
>
> -10. TODO
> +10. OOM Control
> +
> +Memory controler implements oom notifier using cgroup notification
> +API (See cgroups.txt). It allows to register multiple oom notification
> +delivery and gets notification when oom happens.
> +
> +To register a notifier, application need:
> + - create an eventfd using eventfd(2)
> + - open memory.oom_control file
> + - write string like "<event_fd> <memory.oom_control>" to cgroup.event_control
> +
> +Application will be notifier through eventfd when oom happens.
> +OOM notification doesn't work for root cgroup.
> +
> +
> +11. TODO
>
>  1. Add support for accounting huge pages (as a separate controller)
>  2. Make per-cgroup scanner reclaim not-shared pages first
>
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