Re: [PATCH v2 1/8] memcg: accounting for fib6_nodes cache

[Shakeel Butt <shakeelb@google.com>]

On Mon, Mar 15, 2021 at 10:09 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Mon, 15 Mar 2021 15:23:00 +0300 Vasily Averin wrote:
> > An untrusted netadmin inside a memcg-limited container can create a
> > huge number of routing entries. Currently, allocated kernel objects
> > are not accounted to proper memcg, so this can lead to global memory
> > shortage on the host and cause lot of OOM kiils.
> >
> > One such object is the 'struct fib6_node' mostly allocated in
> > net/ipv6/route.c::__ip6_ins_rt() inside the lock_bh()/unlock_bh() section:
> >
> >  write_lock_bh(&table->tb6_lock);
> >  err = fib6_add(&table->tb6_root, rt, info, mxc);
> >  write_unlock_bh(&table->tb6_lock);
> >
> > It this case is not enough to simply add SLAB_ACCOUNT to corresponding
> > kmem cache. The proper memory cgroup still cannot be found due to the
> > incorrect 'in_interrupt()' check used in memcg_kmem_bypass().
> > To be sure that caller is not executed in process contxt
> > '!in_task()' check should be used instead
>
> Sorry for a random question, I didn't get the cover letter.
>
> What's the overhead of adding SLAB_ACCOUNT?
>

The potential overhead is for MEMCG users where we need to
charge/account each allocation from SLAB_ACCOUNT kmem caches. However
charging is done in batches, so the cost is amortized. If there is a
concern about a specific workload then it would be good to see the
impact of this patch for that workload.

> Please make sure you CC netdev on series which may impact networking.