Re: [PATCH] mm: memcg/slab: introduce mem_cgroup_from_obj()

[Shakeel Butt <shakeelb@google.com>]

On Fri, Jan 17, 2020 at 12:36 PM Roman Gushchin <guro@fb.com> wrote:
>
> Sometimes we need to get a memcg pointer from a charged kernel object.
> The right way to get it depends on whether it's a proper slab object
> or it's backed by raw pages (e.g. it's a vmalloc alloction). In the
> first case the kmem_cache->memcg_params.memcg indirection should be
> used; in other cases it's just page->mem_cgroup.
>
> To simplify this task and hide the implementation details let's
> introduce a mem_cgroup_from_obj() helper, which takes a pointer
> to any kernel object and returns a valid memcg pointer or NULL.
>
> Passing a kernel address rather than a pointer to a page will allow
> to use this helper for per-object (rather than per-page) tracked
> objects in the future.
>
> The caller is still responsible to ensure that the returned memcg
> isn't going away underneath: take the rcu read lock, cgroup mutex etc;
> depending on the context.
>
> mem_cgroup_from_kmem() defined in mm/list_lru.c is now obsolete
> and can be removed.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Acked-by: Yafang Shao <laoar.shao@gmail.com>

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