Re: [v7 PATCH 06/12] mm: vmscan: add shrinker_info_protected() helper

From: Roman Gushchin <guro@fb.com>
To: Yang Shi <shy828301@gmail.com>
Cc: <ktkhai@virtuozzo.com>, <vbabka@suse.cz>, <shakeelb@google.com>,
	<david@fromorbit.com>, <hannes@cmpxchg.org>, <mhocko@suse.com>,
	<akpm@linux-foundation.org>, <linux-mm@kvack.org>,
	<linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [v7 PATCH 06/12] mm: vmscan: add shrinker_info_protected() helper
Date: Tue, 9 Feb 2021 16:22:18 -0800	[thread overview]
Message-ID: <20210210002218.GJ524633@carbon.DHCP.thefacebook.com> (raw)
In-Reply-To: <20210209174646.1310591-7-shy828301@gmail.com>

On Tue, Feb 09, 2021 at 09:46:40AM -0800, Yang Shi wrote:
> The shrinker_info is dereferenced in a couple of places via rcu_dereference_protected
> with different calling conventions, for example, using mem_cgroup_nodeinfo helper
> or dereferencing memcg->nodeinfo[nid]->shrinker_info.  And the later patch
> will add more dereference places.
> 
> So extract the dereference into a helper to make the code more readable.  No
> functional change.
> 
> Signed-off-by: Yang Shi <shy828301@gmail.com>
> ---
>  mm/vmscan.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 9436f9246d32..273efbf4d53c 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -190,6 +190,13 @@ static int shrinker_nr_max;
>  #define NR_MAX_TO_SHR_MAP_SIZE(nr_max) \
>  	(DIV_ROUND_UP(nr_max, BITS_PER_LONG) * sizeof(unsigned long))
>  
> +static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
> +						     int nid)
> +{
> +	return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
> +					 lockdep_is_held(&shrinker_rwsem));
> +}
> +

I'd probably drop the "protected" suffix (because there is no unprotected version,
right?).

Other than that LGTM.

Acked-by: Roman Gushchin <guro@fb.com>