Re: [RFC] [PATCH] memcg: cleanup memory thresholds
From: Paul Menage
Date: Mon May 17 2010 - 16:18:01 EST
On Sat, May 8, 2010 at 5:11 PM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
Acked-by: Paul Menage <menage@xxxxxxxxxx>
Thanks,
Paul
> ---
> 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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