linux-kernel - Re: [PATCH v6 08/19] mm: memcg/slab: save obj

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Date:   Fri, 19 Jun 2020 17:16:02 -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 08/19] mm: memcg/slab: save obj_cgroup for non-root
 slab objects

On Mon, Jun 8, 2020 at 4:07 PM Roman Gushchin <guro@...com> wrote:
>
> Store the obj_cgroup pointer in the corresponding place of
> page->obj_cgroups for each allocated non-root slab object.
> Make sure that each allocated object holds a reference to obj_cgroup.
>
> Objcg pointer is obtained from the memcg->objcg dereferencing
> in memcg_kmem_get_cache() and passed from pre_alloc_hook to
> post_alloc_hook. Then in case of successful allocation(s) it's
> getting stored in the page->obj_cgroups vector.
>
> The objcg obtaining part look a bit bulky now, but it will be simplified
> by next commits in the series.
>
> Signed-off-by: Roman Gushchin <guro@...com>
> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>

One nit below otherwise:

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

> ---
[snip]
> +static inline void memcg_slab_post_alloc_hook(struct kmem_cache *s,
> +                                             struct obj_cgroup *objcg,
> +                                             size_t size, void **p)
> +{
> +       struct page *page;
> +       unsigned long off;
> +       size_t i;
> +
> +       for (i = 0; i < size; i++) {
> +               if (likely(p[i])) {
> +                       page = virt_to_head_page(p[i]);
> +                       off = obj_to_index(s, page, p[i]);
> +                       obj_cgroup_get(objcg);
> +                       page_obj_cgroups(page)[off] = objcg;
> +               }
> +       }
> +       obj_cgroup_put(objcg);

Nit: we get the objcg reference in memcg_kmem_get_cache(), doesn't it
look cleaner to put that reference in memcg_kmem_put_cache() instead
of here.

> +       memcg_kmem_put_cache(s);
> +}
> +