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From: Johannes Weiner <hannes@cmpxchg.org>
To: Yang Shi <shy828301@gmail.com>
Cc: guro@fb.com, ktkhai@virtuozzo.com, shakeelb@google.com,
	david@fromorbit.com, mhocko@suse.com, akpm@linux-foundation.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/9] mm: memcontrol: add per memcg shrinker nr_deferred
Date: Thu, 10 Dec 2020 16:33:56 +0100	[thread overview]
Message-ID: <20201210153356.GE264602@cmpxchg.org> (raw)
In-Reply-To: <20201202182725.265020-6-shy828301@gmail.com>

On Wed, Dec 02, 2020 at 10:27:21AM -0800, Yang Shi wrote:
> @@ -504,6 +577,34 @@ int memcg_expand_shrinker_maps(int new_id)
>  	return ret;
>  }
>  
> +int memcg_expand_shrinker_deferred(int new_id)
> +{
> +	int size, old_size, ret = 0;
> +	struct mem_cgroup *memcg;
> +
> +	size = (new_id + 1) * sizeof(atomic_long_t);
> +	old_size = memcg_shrinker_deferred_size;
> +	if (size <= old_size)
> +		return 0;
> +
> +	mutex_lock(&memcg_shrinker_mutex);

The locking is somewhat confusing. I was wondering why we first read
memcg_shrinker_deferred_size "locklessly", then change it while
holding the &memcg_shrinker_mutex.

memcg_shrinker_deferred_size only changes under shrinker_rwsem(write),
correct? This should be documented in a comment, IMO.

memcg_shrinker_mutex looks superfluous then. The memcg allocation path
is the read-side of memcg_shrinker_deferred_size, and so simply needs
to take shrinker_rwsem(read) to lock out shrinker (de)registration.

Also, isn't memcg_shrinker_deferred_size just shrinker_nr_max? And
memcg_expand_shrinker_deferred() is only called when size >= old_size
in the first place (because id >= shrinker_nr_max)?

  parent reply	other threads:[~2020-12-10 15:37 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-02 18:27 [RFC PATCH 0/9] Make shrinker's nr_deferred memcg aware Yang Shi
2020-12-02 18:27 ` [PATCH 1/9] mm: vmscan: simplify nr_deferred update code Yang Shi
2020-12-03  2:56   ` Roman Gushchin
2020-12-02 18:27 ` [PATCH 2/9] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
2020-12-03  3:13   ` Xiaqing (A)
2020-12-11 19:20     ` Yang Shi
2020-12-02 18:27 ` [PATCH 3/9] mm: memcontrol: rename memcg_shrinker_map_mutex to memcg_shrinker_mutex Yang Shi
2020-12-02 18:27 ` [PATCH 4/9] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
2020-12-03  3:01   ` Roman Gushchin
2020-12-03  4:59     ` Yang Shi
2020-12-03 20:08       ` Roman Gushchin
2020-12-03 22:25         ` Yang Shi
2020-12-04 18:52           ` Johannes Weiner
2020-12-04 21:24             ` Yang Shi
2020-12-02 18:27 ` [PATCH 5/9] mm: memcontrol: add per memcg shrinker nr_deferred Yang Shi
2020-12-03  3:06   ` Roman Gushchin
2020-12-03  4:54     ` Yang Shi
2020-12-03 18:03       ` Yang Shi
2020-12-03 20:07         ` Roman Gushchin
2020-12-03 22:49           ` Yang Shi
2020-12-03 23:30             ` Roman Gushchin
2020-12-04  0:22               ` Yang Shi
2020-12-10 15:33   ` Johannes Weiner [this message]
2020-12-10 19:12     ` Yang Shi
2020-12-11 17:52       ` Yang Shi
2020-12-10 21:59     ` Yang Shi
2020-12-02 18:27 ` [PATCH 6/9] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
2020-12-03  3:08   ` Roman Gushchin
2020-12-03  5:01     ` Yang Shi
2020-12-03 11:40   ` Kirill Tkhai
2020-12-08 17:13     ` Yang Shi
2020-12-09 15:41       ` Kirill Tkhai
2020-12-09 17:32         ` Yang Shi
2020-12-10 15:13           ` Johannes Weiner
2020-12-10 15:17             ` Kirill Tkhai
2020-12-15 16:44               ` Johannes Weiner
2020-12-02 18:27 ` [PATCH 7/9] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
2020-12-02 18:27 ` [PATCH 8/9] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
2020-12-02 18:27 ` [PATCH 9/9] mm: vmscan: shrink deferred objects proportional to priority Yang Shi
2020-12-03  2:52 ` [RFC PATCH 0/9] Make shrinker's nr_deferred memcg aware Roman Gushchin
2020-12-03 17:52   ` Yang Shi

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