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

[Shakeel Butt]

On Sat, Apr 24, 2021 at 4:54 AM Vasily Averin <vvs@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Vasily Averin <vvs@xxxxxxxxxxxxx>
> Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
> Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
> Acked-by: Roman Gushchin <guro@xxxxxx>

Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>