On Thu, Mar 11, 2010 at 9:57 AM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
quoted text
> 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/)
>
> TODO:
>  - add a knob to disable oom-kill under a memcg.
>  - add read/write function to oom_control
>
> Changelog: 20100309
>  - splitted from threshold functions. use list rather than array.
>  - moved all to inside of mutex.
> Changelog: 20100304
>  - renewed implemenation.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Looks great! Two remarks below.

Reviewed-by: Kirill A. Shutemov <kirill@shutemov.name>

quoted text
> ---
>  Documentation/cgroups/memory.txt |   20 +++++++
>  mm/memcontrol.c                  |  105 ++++++++++++++++++++++++++++++++++++---
>  2 files changed, 116 insertions(+), 9 deletions(-)
>
> Index: mmotm-2.6.34-Mar9/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.34-Mar9.orig/mm/memcontrol.c
> +++ mmotm-2.6.34-Mar9/mm/memcontrol.c
> @@ -149,6 +149,7 @@ struct mem_cgroup_threshold {
>        u64 threshold;
>  };
>
> +/* For threshold */
>  struct mem_cgroup_threshold_ary {
>        /* An array index points to threshold just below usage. */
>        atomic_t current_threshold;
> @@ -157,8 +158,14 @@ struct mem_cgroup_threshold_ary {
>        /* Array of thresholds */
>        struct mem_cgroup_threshold entries[0];
>  };
> +/* for OOM */
> +struct mem_cgroup_eventfd_list {
> +       struct list_head list;
> +       struct eventfd_ctx *eventfd;
> +};
>
>  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 +227,9 @@ struct mem_cgroup {
>        /* thresholds for mem+swap usage. RCU-protected */
>        struct mem_cgroup_threshold_ary *memsw_thresholds;
>
> +       /* For oom notifier event fd */
> +       struct list_head 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 +292,12 @@ 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
> @@ -1351,6 +1364,8 @@ bool mem_cgroup_handle_oom(struct mem_cg
>         */
>        if (!locked)
>                prepare_to_wait(&memcg_oom_waitq, &owait.wait, TASK_KILLABLE);
> +       else
> +               mem_cgroup_oom_notify(mem);
>        mutex_unlock(&memcg_oom_mutex);
>
>        if (locked)
> @@ -3398,8 +3413,22 @@ static int compare_thresholds(const void
>        return _a->threshold - _b->threshold;
>  }
>
> -static int mem_cgroup_register_event(struct cgroup *cgrp, struct cftype *cft,
> -               struct eventfd_ctx *eventfd, const char *args)
> +static int mem_cgroup_oom_notify_cb(struct mem_cgroup *mem, void *data)
> +{
> +       struct mem_cgroup_eventfd_list *ev;
> +
> +       list_for_each_entry(ev, &mem->oom_notify, list)
> +               eventfd_signal(ev->eventfd, 1);
> +       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_usage_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;
> @@ -3483,8 +3512,8 @@ unlock:
>        return ret;
>  }
>
> -static int mem_cgroup_unregister_event(struct cgroup *cgrp, struct cftype *cft,
> -               struct eventfd_ctx *eventfd)
> +static int mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
> +       struct cftype *cft, struct eventfd_ctx *eventfd)
>  {
>        struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
>        struct mem_cgroup_threshold_ary *thresholds, *thresholds_new;
> @@ -3568,13 +3597,66 @@ unlock:
>        return ret;
>  }
>
> +static int mem_cgroup_oom_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_eventfd_list *event;
> +       int type = MEMFILE_TYPE(cft->private);
> +       int ret = -ENOMEM;
> +
> +       BUG_ON(type != _OOM_TYPE);
> +
> +       mutex_lock(&memcg_oom_mutex);
> +
> +       /* Allocate memory for new array of thresholds */

Irrelevant comment?

quoted text
> +       event = kmalloc(sizeof(*event), GFP_KERNEL);
> +       if (!event)
> +               goto unlock;
> +       /* Add new threshold */

Ditto.

quoted text
> +       event->eventfd = eventfd;
> +       list_add(&event->list, &memcg->oom_notify);
> +
> +       /* already in OOM ? */
> +       if (atomic_read(&memcg->oom_lock))
> +               eventfd_signal(eventfd, 1);
> +       ret = 0;
> +unlock:
> +       mutex_unlock(&memcg_oom_mutex);
> +
> +       return ret;
> +}
> +
> +static int mem_cgroup_oom_unregister_event(struct cgroup *cgrp,
> +       struct cftype *cft, struct eventfd_ctx *eventfd)
> +{
> +       struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);
> +       struct mem_cgroup_eventfd_list *ev, *tmp;
> +       int type = MEMFILE_TYPE(cft->private);
> +
> +       BUG_ON(type != _OOM_TYPE);
> +
> +       mutex_lock(&memcg_oom_mutex);
> +
> +       list_for_each_entry_safe(ev, tmp, &mem->oom_notify, list) {
> +               if (ev->eventfd == eventfd) {
> +                       list_del(&ev->list);
> +                       kfree(ev);
> +               }
> +       }
> +
> +       mutex_unlock(&memcg_oom_mutex);
> +
> +       return 0;
> +}
> +
>  static struct cftype mem_cgroup_files[] = {
>        {
>                .name = "usage_in_bytes",
>                .private = MEMFILE_PRIVATE(_MEM, RES_USAGE),
>                .read_u64 = mem_cgroup_read,
> -               .register_event = mem_cgroup_register_event,
> -               .unregister_event = mem_cgroup_unregister_event,
> +               .register_event = mem_cgroup_usage_register_event,
> +               .unregister_event = mem_cgroup_usage_unregister_event,
>        },
>        {
>                .name = "max_usage_in_bytes",
> @@ -3623,6 +3705,12 @@ 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_oom_register_event,
> +               .unregister_event = mem_cgroup_oom_unregister_event,
> +               .private = MEMFILE_PRIVATE(_OOM_TYPE, OOM_CONTROL),
> +       },
>  };
>
>  #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
> @@ -3631,8 +3719,8 @@ static struct cftype memsw_cgroup_files[
>                .name = "memsw.usage_in_bytes",
>                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_USAGE),
>                .read_u64 = mem_cgroup_read,
> -               .register_event = mem_cgroup_register_event,
> -               .unregister_event = mem_cgroup_unregister_event,
> +               .register_event = mem_cgroup_usage_register_event,
> +               .unregister_event = mem_cgroup_usage_unregister_event,
>        },
>        {
>                .name = "memsw.max_usage_in_bytes",
> @@ -3876,6 +3964,7 @@ mem_cgroup_create(struct cgroup_subsys *
>        }
>        mem->last_scanned_child = 0;
>        spin_lock_init(&mem->reclaim_param_lock);
> +       INIT_LIST_HEAD(&mem->oom_notify);
>
>        if (parent)
>                mem->swappiness = get_swappiness(parent);
> Index: mmotm-2.6.34-Mar9/Documentation/cgroups/memory.txt
> ===================================================================
> --- mmotm-2.6.34-Mar9.orig/Documentation/cgroups/memory.txt
> +++ mmotm-2.6.34-Mar9/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
> @@ -488,7 +491,22 @@ 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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