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Date: Tue, 23 Sep 2014 20:00:23 +0200
From: Michal Hocko <mhocko@...e.cz>
To: Vladimir Davydov <vdavydov@...allels.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Johannes Weiner <hannes@...xchg.org>,
Christoph Lameter <cl@...ux.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH v2 2/3] memcg: don't call memcg_update_all_caches if new
cache id fits
On Mon 22-09-14 20:00:45, Vladimir Davydov wrote:
> memcg_update_all_caches grows arrays of per-memcg caches, so we only
> need to call it when memcg_limited_groups_array_size is increased.
> However, currently we invoke it each time a new kmem-active memory
> cgroup is created. Then it just iterates over all slab_caches and does
> nothinng (memcg_update_cache_size returns immediately).
>
> This patch fixes this insanity. In the meantime it moves the code
> dealing with id allocations to separate functions, memcg_alloc_cache_id
> and memcg_free_cache_id.
>
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
OK, looks good to me
Acked-by: Michal Hocko <mhocko@...e.cz>
Thanks!
> ---
> mm/memcontrol.c | 136 +++++++++++++++++++++++++++++--------------------------
> 1 file changed, 72 insertions(+), 64 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b6bbb1e3e2ab..55d131645b45 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -646,11 +646,13 @@ int memcg_limited_groups_array_size;
> struct static_key memcg_kmem_enabled_key;
> EXPORT_SYMBOL(memcg_kmem_enabled_key);
>
> +static void memcg_free_cache_id(int id);
> +
> static void disarm_kmem_keys(struct mem_cgroup *memcg)
> {
> if (memcg_kmem_is_active(memcg)) {
> static_key_slow_dec(&memcg_kmem_enabled_key);
> - ida_simple_remove(&kmem_limited_groups, memcg->kmemcg_id);
> + memcg_free_cache_id(memcg->kmemcg_id);
> }
> /*
> * This check can't live in kmem destruction function,
> @@ -2892,19 +2894,44 @@ int memcg_cache_id(struct mem_cgroup *memcg)
> return memcg ? memcg->kmemcg_id : -1;
> }
>
> -static size_t memcg_caches_array_size(int num_groups)
> +static int memcg_alloc_cache_id(void)
> {
> - ssize_t size;
> - if (num_groups <= 0)
> - return 0;
> + int id, size;
> + int err;
> +
> + id = ida_simple_get(&kmem_limited_groups,
> + 0, MEMCG_CACHES_MAX_SIZE, GFP_KERNEL);
> + if (id < 0)
> + return id;
>
> - size = 2 * num_groups;
> + if (id < memcg_limited_groups_array_size)
> + return id;
> +
> + /*
> + * There's no space for the new id in memcg_caches arrays,
> + * so we have to grow them.
> + */
> +
> + size = 2 * (id + 1);
> if (size < MEMCG_CACHES_MIN_SIZE)
> size = MEMCG_CACHES_MIN_SIZE;
> else if (size > MEMCG_CACHES_MAX_SIZE)
> size = MEMCG_CACHES_MAX_SIZE;
>
> - return size;
> + mutex_lock(&memcg_slab_mutex);
> + err = memcg_update_all_caches(size);
> + mutex_unlock(&memcg_slab_mutex);
> +
> + if (err) {
> + ida_simple_remove(&kmem_limited_groups, id);
> + return err;
> + }
> + return id;
> +}
> +
> +static void memcg_free_cache_id(int id)
> +{
> + ida_simple_remove(&kmem_limited_groups, id);
> }
>
> /*
> @@ -2914,59 +2941,55 @@ static size_t memcg_caches_array_size(int num_groups)
> */
> void memcg_update_array_size(int num)
> {
> - if (num > memcg_limited_groups_array_size)
> - memcg_limited_groups_array_size = memcg_caches_array_size(num);
> + memcg_limited_groups_array_size = num;
> }
>
> int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
> {
> struct memcg_cache_params *cur_params = s->memcg_params;
> + struct memcg_cache_params *new_params;
> + size_t size;
> + int i;
>
> VM_BUG_ON(!is_root_cache(s));
>
> - if (num_groups > memcg_limited_groups_array_size) {
> - int i;
> - struct memcg_cache_params *new_params;
> - ssize_t size = memcg_caches_array_size(num_groups);
> + size = num_groups * sizeof(void *);
> + size += offsetof(struct memcg_cache_params, memcg_caches);
>
> - size *= sizeof(void *);
> - size += offsetof(struct memcg_cache_params, memcg_caches);
> -
> - new_params = kzalloc(size, GFP_KERNEL);
> - if (!new_params)
> - return -ENOMEM;
> -
> - new_params->is_root_cache = true;
> + new_params = kzalloc(size, GFP_KERNEL);
> + if (!new_params)
> + return -ENOMEM;
>
> - /*
> - * There is the chance it will be bigger than
> - * memcg_limited_groups_array_size, if we failed an allocation
> - * in a cache, in which case all caches updated before it, will
> - * have a bigger array.
> - *
> - * But if that is the case, the data after
> - * memcg_limited_groups_array_size is certainly unused
> - */
> - for (i = 0; i < memcg_limited_groups_array_size; i++) {
> - if (!cur_params->memcg_caches[i])
> - continue;
> - new_params->memcg_caches[i] =
> - cur_params->memcg_caches[i];
> - }
> + new_params->is_root_cache = true;
>
> - /*
> - * Ideally, we would wait until all caches succeed, and only
> - * then free the old one. But this is not worth the extra
> - * pointer per-cache we'd have to have for this.
> - *
> - * It is not a big deal if some caches are left with a size
> - * bigger than the others. And all updates will reset this
> - * anyway.
> - */
> - rcu_assign_pointer(s->memcg_params, new_params);
> - if (cur_params)
> - kfree_rcu(cur_params, rcu_head);
> + /*
> + * There is the chance it will be bigger than
> + * memcg_limited_groups_array_size, if we failed an allocation
> + * in a cache, in which case all caches updated before it, will
> + * have a bigger array.
> + *
> + * But if that is the case, the data after
> + * memcg_limited_groups_array_size is certainly unused
> + */
> + for (i = 0; i < memcg_limited_groups_array_size; i++) {
> + if (!cur_params->memcg_caches[i])
> + continue;
> + new_params->memcg_caches[i] =
> + cur_params->memcg_caches[i];
> }
> +
> + /*
> + * Ideally, we would wait until all caches succeed, and only
> + * then free the old one. But this is not worth the extra
> + * pointer per-cache we'd have to have for this.
> + *
> + * It is not a big deal if some caches are left with a size
> + * bigger than the others. And all updates will reset this
> + * anyway.
> + */
> + rcu_assign_pointer(s->memcg_params, new_params);
> + if (cur_params)
> + kfree_rcu(cur_params, rcu_head);
> return 0;
> }
>
> @@ -4167,23 +4190,12 @@ static int __memcg_activate_kmem(struct mem_cgroup *memcg,
> if (err)
> goto out;
>
> - memcg_id = ida_simple_get(&kmem_limited_groups,
> - 0, MEMCG_CACHES_MAX_SIZE, GFP_KERNEL);
> + memcg_id = memcg_alloc_cache_id();
> if (memcg_id < 0) {
> err = memcg_id;
> goto out;
> }
>
> - /*
> - * Make sure we have enough space for this cgroup in each root cache's
> - * memcg_params.
> - */
> - mutex_lock(&memcg_slab_mutex);
> - err = memcg_update_all_caches(memcg_id + 1);
> - mutex_unlock(&memcg_slab_mutex);
> - if (err)
> - goto out_rmid;
> -
> memcg->kmemcg_id = memcg_id;
> INIT_LIST_HEAD(&memcg->memcg_slab_caches);
>
> @@ -4204,10 +4216,6 @@ static int __memcg_activate_kmem(struct mem_cgroup *memcg,
> out:
> memcg_resume_kmem_account();
> return err;
> -
> -out_rmid:
> - ida_simple_remove(&kmem_limited_groups, memcg_id);
> - goto out;
> }
>
> static int memcg_activate_kmem(struct mem_cgroup *memcg,
> --
> 1.7.10.4
>
--
Michal Hocko
SUSE Labs
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