Re: [PATCH v6 09/19] mm: memcg/slab: charge individual slab objects instead of pages

[Shakeel Butt <shakeelb@google.com>]

On Mon, Jun 8, 2020 at 4:07 PM Roman Gushchin <guro@fb.com> wrote:
>
> Switch to per-object accounting of non-root slab objects.
>
> Charging is performed using obj_cgroup API in the pre_alloc hook.
> Obj_cgroup is charged with the size of the object and the size
> of metadata: as now it's the size of an obj_cgroup pointer.
> If the amount of memory has been charged successfully, the actual
> allocation code is executed. Otherwise, -ENOMEM is returned.
>
> In the post_alloc hook if the actual allocation succeeded,
> corresponding vmstats are bumped and the obj_cgroup pointer is saved.
> Otherwise, the charge is canceled.
>
> On the free path obj_cgroup pointer is obtained and used to uncharge
> the size of the releasing object.
>
> Memcg and lruvec counters are now representing only memory used
> by active slab objects and do not include the free space. The free
> space is shared and doesn't belong to any specific cgroup.
>
> Global per-node slab vmstats are still modified from (un)charge_slab_page()
> functions. The idea is to keep all slab pages accounted as slab pages
> on system level.
>
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
> ---
[snip]
> +
> +static inline struct kmem_cache *memcg_slab_pre_alloc_hook(struct kmem_cache *s,
> +                                               struct obj_cgroup **objcgp,
> +                                               size_t objects, gfp_t flags)
> +{
> +       struct kmem_cache *cachep;
> +
> +       cachep = memcg_kmem_get_cache(s, objcgp);
> +       if (is_root_cache(cachep))
> +               return s;
> +
> +       if (obj_cgroup_charge(*objcgp, flags, objects * obj_full_size(s))) {
> +               memcg_kmem_put_cache(cachep);

obj_cgroup_put(objcgp)? Or better to do that in memcg_kmem_put_cache().

> +               cachep = NULL;
> +       }
> +
> +       return cachep;
> +}
> +