[PATCH v2 2/3] memcg: don't call memcg_update_all_caches if new cache id fits

From: Vladimir Davydov
Date: Mon Sep 22 2014 - 12:01:07 EST

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@xxxxxxxxxxxxx>
---
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

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