linux-kernel - Re: [PATCH v6 06/19] mm: memcg/slab: obj

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Message-ID: <CALvZod4-hsXx6GcrftsXtMA08w9gJ3Sk_Lv0CxzDF20xsyf9JQ@mail.gmail.com>
Date:   Fri, 19 Jun 2020 15:16:44 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Kernel Team <kernel-team@...com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 06/19] mm: memcg/slab: obj_cgroup API

On Fri, Jun 19, 2020 at 2:38 PM Roman Gushchin <guro@...com> wrote:
>
[snip]
> > > memcg->objcg is rcu protected.
> > > objcg->memcg is a raw pointer, which is always pointing at a memory
> > > cgroup, but can be atomically swapped to the parent memory cgroup. So
> > > the caller
> >
> > What type of caller? The allocator?
>
> Basically whoever uses the pointer. Is it better to s/caller/user?
>

Yes 'user' feels better.

> >
[...]
> >
> > The normal stock can go to 32*nr_cpus*PAGE_SIZE. I am wondering if
> > just PAGE_SIZE is too less for obj stock.
>
> It works on top of the current stock of 32 pages, so it can grab these
> 32 pages without any atomic operations. And it should be easy to increase
> this limit if we'll see any benefits.
>
> Thank you for looking into the patchset!
>
> Andrew, can you, please, squash the following fix based on Shakeel's suggestions?
> Thanks!
>
> --

For the following squashed into the original patch:

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

>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 7ed3af71a6fb..2499f78cf32d 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -326,7 +326,7 @@ struct mem_cgroup {
>         int kmemcg_id;
>         enum memcg_kmem_state kmem_state;
>         struct obj_cgroup __rcu *objcg;
> -       struct list_head objcg_list;
> +       struct list_head objcg_list; /* list of inherited objcgs */
>  #endif
>
>  #ifdef CONFIG_CGROUP_WRITEBACK
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 70cd44b28db1..9f14b91700d9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2843,7 +2843,7 @@ __always_inline struct obj_cgroup *get_obj_cgroup_from_current(void)
>         struct obj_cgroup *objcg = NULL;
>         struct mem_cgroup *memcg;
>
> -       if (unlikely(!current->mm))
> +       if (unlikely(!current->mm && !current->active_memcg))
>                 return NULL;
>
>         rcu_read_lock();