linux-kernel - Re: [PATCH v3 1/2] mm/list_lru.c: fix list_lru_count

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Date:   Wed, 28 Jun 2017 20:18:54 +0300
From:   Vladimir Davydov <vdavydov.dev@...il.com>
To:     Sahitya Tummala <stummala@...eaurora.org>
Cc:     Alexander Polakov <apolyakov@...et.ru>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>, viro@...iv.linux.org.uk,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] mm/list_lru.c: fix list_lru_count_node() to be
 race free

On Wed, Jun 28, 2017 at 11:37:23AM +0530, Sahitya Tummala wrote:
> list_lru_count_node() iterates over all memcgs to get
> the total number of entries on the node but it can race with
> memcg_drain_all_list_lrus(), which migrates the entries from
> a dead cgroup to another. This can return incorrect number of
> entries from list_lru_count_node().
> 
> Fix this by keeping track of entries per node and simply return
> it in list_lru_count_node().
> 
> Signed-off-by: Sahitya Tummala <stummala@...eaurora.org>
> ---
>  include/linux/list_lru.h |  1 +
>  mm/list_lru.c            | 14 ++++++--------
>  2 files changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
> index cb0ba9f..eff61bc 100644
> --- a/include/linux/list_lru.h
> +++ b/include/linux/list_lru.h
> @@ -44,6 +44,7 @@ struct list_lru_node {
>  	/* for cgroup aware lrus points to per cgroup lists, otherwise NULL */
>  	struct list_lru_memcg	*memcg_lrus;
>  #endif
> +	long nr_count;

'nr_count' sounds awkward. I think it should be called 'nr_items'.

Other than that, looks good to me.