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Subject: Re: [PATCH v3 08/19] mm: memcg/slab: save obj_cgroup for non-root
 slab objects
To:     Roman Gushchin <guro@fb.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>, linux-mm@kvack.org,
        kernel-team@fb.com, linux-kernel@vger.kernel.org
References: <20200422204708.2176080-1-guro@fb.com>
 <20200422204708.2176080-9-guro@fb.com>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <3e02b3c6-2bf5-bddb-d855-83a1a1a54034@suse.cz>
Date:   Mon, 25 May 2020 17:07:22 +0200
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On 4/22/20 10:46 PM, Roman Gushchin 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@fb.com>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>

Nit below:

> diff --git a/mm/slab.h b/mm/slab.h
> index 44def57f050e..525e09e05743 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
...
> @@ -636,8 +684,8 @@ static inline void slab_post_alloc_hook(struct kmem_cache *s, gfp_t flags,
>  					 s->flags, flags);
>  	}
>  
> -	if (memcg_kmem_enabled())
> -		memcg_kmem_put_cache(s);
> +	if (!is_root_cache(s))
> +		memcg_slab_post_alloc_hook(s, objcg, size, p);
>  }
>  
>  #ifndef CONFIG_SLOB

Keep also the memcg_kmem_enabled() static key check, like elsewhere?