Re: [PATCH v3 2/5] mm: memcg/percpu: account percpu memory to memory cgroups

[Shakeel Butt <shakeelb@google.com>]

On Tue, Jun 23, 2020 at 11:47 AM Roman Gushchin <guro@fb.com> wrote:
>
> Percpu memory is becoming more and more widely used by various subsystems,
> and the total amount of memory controlled by the percpu allocator can make
> a good part of the total memory.
>
> As an example, bpf maps can consume a lot of percpu memory, and they are
> created by a user.  Also, some cgroup internals (e.g.  memory controller
> statistics) can be quite large.  On a machine with many CPUs and big
> number of cgroups they can consume hundreds of megabytes.
>
> So the lack of memcg accounting is creating a breach in the memory
> isolation.  Similar to the slab memory, percpu memory should be accounted
> by default.
>
> To implement the perpcu accounting it's possible to take the slab memory
> accounting as a model to follow.  Let's introduce two types of percpu
> chunks: root and memcg.  What makes memcg chunks different is an
> additional space allocated to store memcg membership information.  If
> __GFP_ACCOUNT is passed on allocation, a memcg chunk should be be used.
> If it's possible to charge the corresponding size to the target memory
> cgroup, allocation is performed, and the memcg ownership data is recorded.
> System-wide allocations are performed using root chunks, so there is no
> additional memory overhead.
>
> To implement a fast reparenting of percpu memory on memcg removal, we
> don't store mem_cgroup pointers directly: instead we use obj_cgroup API,
> introduced for slab accounting.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Acked-by: Dennis Zhou <dennis@kernel.org>

Reviewed-by: Shakeel Butt <shakeelb@google.com>