Any comments?

On Sun, May 9, 2010 at 3:11 AM, Kirill A. Shutemov <kirill@shutemov.name> wrote:
> Introduce struct mem_cgroup_thresholds. It helps to reduce number of
> checks of thresholds type (memory or mem+swap).
>
> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> ---
>  mm/memcontrol.c |  151 ++++++++++++++++++++++++-------------------------------
>  1 files changed, 66 insertions(+), 85 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index a6d2a4c..a6c6268 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -158,6 +158,18 @@ struct mem_cgroup_threshold_ary {
>        /* Array of thresholds */
>        struct mem_cgroup_threshold entries[0];
>  };
> +
> +struct mem_cgroup_thresholds {
> +       /* Primary thresholds array */
> +       struct mem_cgroup_threshold_ary *primary;
> +       /*
> +        * Spare threshold array.
> +        * It needed to make mem_cgroup_unregister_event() "never fail".
> +        * It must be able to store at least primary->size - 1 entires.
> +        */
> +       struct mem_cgroup_threshold_ary *spare;
> +};
> +
>  /* for OOM */
>  struct mem_cgroup_eventfd_list {
>        struct list_head list;
> @@ -224,20 +236,10 @@ struct mem_cgroup {
>        struct mutex thresholds_lock;
>
>        /* thresholds for memory usage. RCU-protected */
> -       struct mem_cgroup_threshold_ary *thresholds;
> -
> -       /*
> -        * Preallocated buffer to be used in mem_cgroup_unregister_event()
> -        * to make it "never fail".
> -        * It must be able to store at least thresholds->size - 1 entries.
> -        */
> -       struct mem_cgroup_threshold_ary *__thresholds;
> +       struct mem_cgroup_thresholds thresholds;
>
>        /* thresholds for mem+swap usage. RCU-protected */
> -       struct mem_cgroup_threshold_ary *memsw_thresholds;
> -
> -       /* the same as __thresholds, but for memsw_thresholds */
> -       struct mem_cgroup_threshold_ary *__memsw_thresholds;
> +       struct mem_cgroup_thresholds memsw_thresholds;
>
>        /* For oom notifier event fd */
>        struct list_head oom_notify;
> @@ -3438,9 +3440,9 @@ static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
>
>        rcu_read_lock();
>        if (!swap)
> -               t = rcu_dereference(memcg->thresholds);
> +               t = rcu_dereference(memcg->thresholds.primary);
>        else
> -               t = rcu_dereference(memcg->memsw_thresholds);
> +               t = rcu_dereference(memcg->memsw_thresholds.primary);
>
>        if (!t)
>                goto unlock;
> @@ -3514,91 +3516,78 @@ 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;
> +       struct mem_cgroup_thresholds *thresholds;
> +       struct mem_cgroup_threshold_ary *new;
>        int type = MEMFILE_TYPE(cft->private);
>        u64 threshold, usage;
> -       int size;
> -       int i, ret;
> +       int i, size, ret;
>
>        ret = res_counter_memparse_write_strategy(args, &threshold);
>        if (ret)
>                return ret;
>
>        mutex_lock(&memcg->thresholds_lock);
> +
>        if (type == _MEM)
> -               thresholds = memcg->thresholds;
> +               thresholds = &memcg->thresholds;
>        else if (type == _MEMSWAP)
> -               thresholds = memcg->memsw_thresholds;
> +               thresholds = &memcg->memsw_thresholds;
>        else
>                BUG();
>
>        usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
>
>        /* Check if a threshold crossed before adding a new one */
> -       if (thresholds)
> +       if (thresholds->primary)
>                __mem_cgroup_threshold(memcg, type == _MEMSWAP);
>
> -       if (thresholds)
> -               size = thresholds->size + 1;
> -       else
> -               size = 1;
> +       size = thresholds->primary ? thresholds->primary->size + 1 : 1;
>
>        /* Allocate memory for new array of thresholds */
> -       thresholds_new = kmalloc(sizeof(*thresholds_new) +
> -                       size * sizeof(struct mem_cgroup_threshold),
> +       new = kmalloc(sizeof(*new) + size * sizeof(struct mem_cgroup_threshold),
>                        GFP_KERNEL);
> -       if (!thresholds_new) {
> +       if (!new) {
>                ret = -ENOMEM;
>                goto unlock;
>        }
> -       thresholds_new->size = size;
> +       new->size = size;
>
>        /* Copy thresholds (if any) to new array */
> -       if (thresholds)
> -               memcpy(thresholds_new->entries, thresholds->entries,
> -                               thresholds->size *
> +       if (thresholds->primary) {
> +               memcpy(new->entries, thresholds->primary->entries, (size - 1) *
>                                sizeof(struct mem_cgroup_threshold));
> +       }
> +
>        /* Add new threshold */
> -       thresholds_new->entries[size - 1].eventfd = eventfd;
> -       thresholds_new->entries[size - 1].threshold = threshold;
> +       new->entries[size - 1].eventfd = eventfd;
> +       new->entries[size - 1].threshold = threshold;
>
>        /* Sort thresholds. Registering of new threshold isn't time-critical */
> -       sort(thresholds_new->entries, size,
> -                       sizeof(struct mem_cgroup_threshold),
> +       sort(new->entries, size, sizeof(struct mem_cgroup_threshold),
>                        compare_thresholds, NULL);
>
>        /* Find current threshold */
> -       thresholds_new->current_threshold = -1;
> +       new->current_threshold = -1;
>        for (i = 0; i < size; i++) {
> -               if (thresholds_new->entries[i].threshold < usage) {
> +               if (new->entries[i].threshold < usage) {
>                        /*
> -                        * thresholds_new->current_threshold will not be used
> -                        * until rcu_assign_pointer(), so it's safe to increment
> +                        * new->current_threshold will not be used until
> +                        * rcu_assign_pointer(), so it's safe to increment
>                         * it here.
>                         */
> -                       ++thresholds_new->current_threshold;
> +                       ++new->current_threshold;
>                }
>        }
>
> -       if (type == _MEM)
> -               rcu_assign_pointer(memcg->thresholds, thresholds_new);
> -       else
> -               rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
> +       /* Free old spare buffer and save old primary buffer as spare */
> +       kfree(thresholds->spare);
> +       thresholds->spare = thresholds->primary;
> +
> +       rcu_assign_pointer(thresholds->primary, new);
>
>        /* To be sure that nobody uses thresholds */
>        synchronize_rcu();
>
> -       /*
> -        * Free old preallocated buffer and use thresholds as new
> -        * preallocated buffer.
> -        */
> -       if (type == _MEM) {
> -               kfree(memcg->__thresholds);
> -               memcg->__thresholds = thresholds;
> -       } else {
> -               kfree(memcg->__memsw_thresholds);
> -               memcg->__memsw_thresholds = thresholds;
> -       }
>  unlock:
>        mutex_unlock(&memcg->thresholds_lock);
>
> @@ -3609,17 +3598,17 @@ static void 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;
> +       struct mem_cgroup_thresholds *thresholds;
> +       struct mem_cgroup_threshold_ary *new;
>        int type = MEMFILE_TYPE(cft->private);
>        u64 usage;
> -       int size = 0;
> -       int i, j;
> +       int i, j, size;
>
>        mutex_lock(&memcg->thresholds_lock);
>        if (type == _MEM)
> -               thresholds = memcg->thresholds;
> +               thresholds = &memcg->thresholds;
>        else if (type == _MEMSWAP)
> -               thresholds = memcg->memsw_thresholds;
> +               thresholds = &memcg->memsw_thresholds;
>        else
>                BUG();
>
> @@ -3635,53 +3624,45 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
>        __mem_cgroup_threshold(memcg, type == _MEMSWAP);
>
>        /* Calculate new number of threshold */
> -       for (i = 0; i < thresholds->size; i++) {
> -               if (thresholds->entries[i].eventfd != eventfd)
> +       size = 0;
> +       for (i = 0; i < thresholds->primary->size; i++) {
> +               if (thresholds->primary->entries[i].eventfd != eventfd)
>                        size++;
>        }
>
> -       /* Use preallocated buffer for new array of thresholds */
> -       if (type == _MEM)
> -               thresholds_new = memcg->__thresholds;
> -       else
> -               thresholds_new = memcg->__memsw_thresholds;
> +       new = thresholds->spare;
>
>        /* Set thresholds array to NULL if we don't have thresholds */
>        if (!size) {
> -               kfree(thresholds_new);
> -               thresholds_new = NULL;
> +               kfree(new);
> +               new = NULL;
>                goto swap_buffers;
>        }
>
> -       thresholds_new->size = size;
> +       new->size = size;
>
>        /* Copy thresholds and find current threshold */
> -       thresholds_new->current_threshold = -1;
> -       for (i = 0, j = 0; i < thresholds->size; i++) {
> -               if (thresholds->entries[i].eventfd == eventfd)
> +       new->current_threshold = -1;
> +       for (i = 0, j = 0; i < thresholds->primary->size; i++) {
> +               if (thresholds->primary->entries[i].eventfd == eventfd)
>                        continue;
>
> -               thresholds_new->entries[j] = thresholds->entries[i];
> -               if (thresholds_new->entries[j].threshold < usage) {
> +               new->entries[j] = thresholds->primary->entries[i];
> +               if (new->entries[j].threshold < usage) {
>                        /*
> -                        * thresholds_new->current_threshold will not be used
> +                        * new->current_threshold will not be used
>                         * until rcu_assign_pointer(), so it's safe to increment
>                         * it here.
>                         */
> -                       ++thresholds_new->current_threshold;
> +                       ++new->current_threshold;
>                }
>                j++;
>        }
>
>  swap_buffers:
> -       /* Swap thresholds array and preallocated buffer */
> -       if (type == _MEM) {
> -               memcg->__thresholds = thresholds;
> -               rcu_assign_pointer(memcg->thresholds, thresholds_new);
> -       } else {
> -               memcg->__memsw_thresholds = thresholds;
> -               rcu_assign_pointer(memcg->memsw_thresholds, thresholds_new);
> -       }
> +       /* Swap primary and spare array */
> +       thresholds->spare = thresholds->primary;
> +       rcu_assign_pointer(thresholds->primary, new);
>
>        /* To be sure that nobody uses thresholds */
>        synchronize_rcu();
> --
> 1.7.0.4
>
>
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