Re: [PATCH v2 1/1] memcg: enable accounting for pids in nested pid namespaces

[Vasily Averin <vvs@virtuozzo.com>]

Dear Andrew,
could you please pick up this patch and add
 Reviewed-by: Shakeel Butt <shakeelb@google.com>

Thank you,
	Vasily Averin

On 4/24/21 2:54 PM, Vasily Averin wrote:
> Commit 5d097056c9a0 ("kmemcg: account certain kmem allocations to memcg")
> enabled memcg accounting for pids allocated from init_pid_ns.pid_cachep,
> but forgot to adjust the setting for nested pid namespaces.
> As a result, pid memory is not accounted exactly where it is really needed,
> inside memcg-limited containers with their own pid namespaces.
> 
> Pid was one the first kernel objects enabled for memcg accounting.
> init_pid_ns.pid_cachep marked by SLAB_ACCOUNT and we can expect that
> any new pids in the system are memcg-accounted.
> 
> Though recently I've noticed that it is wrong. nested pid namespaces creates 
> own slab caches for pid objects, nested pids have increased size because contain 
> id both for all parent and for own pid namespaces. The problem is that these slab
> caches are _NOT_ marked by SLAB_ACCOUNT, as a result any pids allocated in 
> nested pid namespaces are not memcg-accounted.
> 
> Pid struct in nested pid namespace consumes up to 500 bytes memory, 
> 100000 such objects gives us up to ~50Mb unaccounted memory,
> this allow container to exceed assigned memcg limits.
> 
> Fixes: 5d097056c9a0 ("kmemcg: account certain kmem allocations to memcg")
> Cc: stable@vger.kernel.org
> Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
> Reviewed-by: Michal Koutný <mkoutny@suse.com>
> Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
> Acked-by: Roman Gushchin <guro@fb.com>
> ---
>  kernel/pid_namespace.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index 6cd6715..a46a372 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -51,7 +51,8 @@ static struct kmem_cache *create_pid_cachep(unsigned int level)
>  	mutex_lock(&pid_caches_mutex);
>  	/* Name collision forces to do allocation under mutex. */
>  	if (!*pkc)
> -		*pkc = kmem_cache_create(name, len, 0, SLAB_HWCACHE_ALIGN, 0);
> +		*pkc = kmem_cache_create(name, len, 0,
> +					 SLAB_HWCACHE_ALIGN | SLAB_ACCOUNT, 0);
>  	mutex_unlock(&pid_caches_mutex);
>  	/* current can fail, but someone else can succeed. */
>  	return READ_ONCE(*pkc);
>