On Thu, 30 Jan 2014 20:01:33 +0400 Vladimir Davydov <[email protected]>
wrote:
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3400,7 +3400,7 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
> static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
> struct kmem_cache *s)
> {
> - struct kmem_cache *new;
> + struct kmem_cache *new = NULL;
> static char *tmp_name = NULL;
> static DEFINE_MUTEX(mutex); /* protects tmp_name */
>
> @@ -3416,7 +3416,7 @@ static struct kmem_cache
> *memcg_create_kmem_cache(struct mem_cgroup *memcg,
> if (!tmp_name) {
> tmp_name = kmalloc(PATH_MAX, GFP_KERNEL);
> if (!tmp_name)
> - return NULL;
> + goto out;
> }
>
> rcu_read_lock();
> @@ -3426,12 +3426,11 @@ static struct kmem_cache
> *memcg_create_kmem_cache(struct mem_cgroup *memcg,
>
> new = kmem_cache_create_memcg(memcg, tmp_name, s->object_size, s->align,
> (s->flags & ~SLAB_PANIC), s->ctor, s);
> -
> if (new)
> new->allocflags |= __GFP_KMEMCG;
> else
> new = s;
> -
> +out:
> mutex_unlock(&mutex);
> return new;
> }
Well gee, how did that one get through?
What was the point in permanently allocating tmp_name, btw? "This
static temporary buffer is used to prevent from pointless shortliving
allocation"? That's daft - memcg_create_kmem_cache() is not a fastpath
and there are a million places in the kernel where we could permanently
leak memory because it is "pointless" to allocate on demand.
The allocation of PATH_MAX bytes is unfortunate - kasprintf() wouild
work well here, but cgroup_name()'s need for rcu_read_lock() screws us
up.
So how about doing this?
From: Andrew Morton <[email protected]>
Subject: mm/memcontrol.c: memcg_create_kmem_cache() tweaks
Allocate tmp_name on demand rather than permanently consuming PATH_MAX
bytes of memory. This permits a small reduction in the mutex hold time as
well.
Cc: Glauber Costa <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
mm/memcontrol.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)
diff -puN mm/memcontrol.c~mm-memcontrolc-memcg_create_kmem_cache-tweaks
mm/memcontrol.c
--- a/mm/memcontrol.c~mm-memcontrolc-memcg_create_kmem_cache-tweaks
+++ a/mm/memcontrol.c
@@ -3401,17 +3401,14 @@ static struct kmem_cache *memcg_create_k
struct kmem_cache *s)
{
struct kmem_cache *new = NULL;
- static char *tmp_name = NULL;
+ static char *tmp_name;
static DEFINE_MUTEX(mutex); /* protects tmp_name */
BUG_ON(!memcg_can_account_kmem(memcg));
- mutex_lock(&mutex);
/*
- * kmem_cache_create_memcg duplicates the given name and
- * cgroup_name for this name requires RCU context.
- * This static temporary buffer is used to prevent from
- * pointless shortliving allocation.
+ * kmem_cache_create_memcg duplicates the given name and cgroup_name()
+ * for this name requires rcu_read_lock().
*/
if (!tmp_name) {
tmp_name = kmalloc(PATH_MAX, GFP_KERNEL);
@@ -3419,6 +3416,7 @@ static struct kmem_cache *memcg_create_k
goto out;
}
+ mutex_lock(&mutex);
rcu_read_lock();
snprintf(tmp_name, PATH_MAX, "%s(%d:%s)", s->name,
memcg_cache_id(memcg), cgroup_name(memcg->css.cgroup));
@@ -3432,6 +3430,7 @@ static struct kmem_cache *memcg_create_k
new = s;
out:
mutex_unlock(&mutex);
+ kfree(tmp_name);
return new;
}
_
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