Message-ID: <bc829246-4606-cc8d-4a4f-da285255f5a3@ya.ru>
Date:   Thu, 9 Mar 2023 01:39:52 +0300
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Subject: Re: [PATCH v4 7/8] mm: vmscan: remove shrinker_rwsem from
 synchronize_shrinkers()
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To:     Qi Zheng <zhengqi.arch@bytedance.com>, akpm@linux-foundation.org,
        hannes@cmpxchg.org, shakeelb@google.com, mhocko@kernel.org,
        roman.gushchin@linux.dev, muchun.song@linux.dev, david@redhat.com,
        shy828301@gmail.com, rppt@kernel.org
Cc:     sultan@kerneltoast.com, dave@stgolabs.net,
        penguin-kernel@I-love.SAKURA.ne.jp, paulmck@kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20230307065605.58209-1-zhengqi.arch@bytedance.com>
 <20230307065605.58209-8-zhengqi.arch@bytedance.com>
From:   Kirill Tkhai <tkhai@ya.ru>
In-Reply-To: <20230307065605.58209-8-zhengqi.arch@bytedance.com>
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On 07.03.2023 09:56, Qi Zheng wrote:
> Now there are no readers of shrinker_rwsem, so
> synchronize_shrinkers() does not need to hold the
> writer of shrinker_rwsem to wait for all running
> shinkers to complete, synchronize_srcu() is enough.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> ---
>  mm/vmscan.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 7aaf6f94ac1b..ac7ab4aa344f 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -796,15 +796,11 @@ EXPORT_SYMBOL(unregister_shrinker);
>  /**
>   * synchronize_shrinkers - Wait for all running shrinkers to complete.
>   *
> - * This is equivalent to calling unregister_shrink() and register_shrinker(),
> - * but atomically and with less overhead. This is useful to guarantee that all
> - * shrinker invocations have seen an update, before freeing memory, similar to
> - * rcu.
> + * This is useful to guarantee that all shrinker invocations have seen an
> + * update, before freeing memory.
>   */
>  void synchronize_shrinkers(void)
>  {
> -	down_write(&shrinker_rwsem);
> -	up_write(&shrinker_rwsem);
>  	atomic_inc(&shrinker_srcu_generation);
>  	synchronize_srcu(&shrinker_srcu);
>  }

Just curious, callers of synchronize_shrinkers() don't want to have parallel register_shrinker() and unregister_shrink() are completed?
Here we only should wait for parallel shrink_slab(), correct?