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From: Vlastimil Babka <vbabka@suse.cz>
To: Yang Shi <shy828301@gmail.com>,
	guro@fb.com, ktkhai@virtuozzo.com, shakeelb@google.com,
	david@fromorbit.com, hannes@cmpxchg.org, mhocko@suse.com,
	akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [v5 PATCH 03/11] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation
Date: Thu, 28 Jan 2021 17:19:08 +0100	[thread overview]
Message-ID: <73c724ba-a1ef-a862-4c31-153d92826f8d@suse.cz> (raw)
In-Reply-To: <20210127233345.339910-4-shy828301@gmail.com>

On 1/28/21 12:33 AM, Yang Shi wrote:
> Since memcg_shrinker_map_size just can be changed under holding shrinker_rwsem
> exclusively, the read side can be protected by holding read lock, so it sounds
> superfluous to have a dedicated mutex.
> 
> Kirill Tkhai suggested use write lock since:
> 
>   * We want the assignment to shrinker_maps is visible for shrink_slab_memcg().
>   * The rcu_dereference_protected() dereferrencing in shrink_slab_memcg(), but
>     in case of we use READ lock in alloc_shrinker_maps(), the dereferrencing
>     is not actually protected.
>   * READ lock makes alloc_shrinker_info() racy against memory allocation fail.
>     alloc_shrinker_info()->free_shrinker_info() may free memory right after
>     shrink_slab_memcg() dereferenced it. You may say
>     shrink_slab_memcg()->mem_cgroup_online() protects us from it? Yes, sure,
>     but this is not the thing we want to remember in the future, since this
>     spreads modularity.
> 
> And a test with heavy paging workload didn't show write lock makes things worse.
> 
> Signed-off-by: Yang Shi <shy828301@gmail.com>

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


  reply	other threads:[~2021-01-28 16:20 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-27 23:33 [v5 PATCH 0/11] Make shrinker's nr_deferred memcg aware Yang Shi
2021-01-27 23:33 ` [v5 PATCH 01/11] mm: vmscan: use nid from shrink_control for tracepoint Yang Shi
2021-01-28 16:02   ` Vlastimil Babka
2021-01-27 23:33 ` [v5 PATCH 02/11] mm: vmscan: consolidate shrinker_maps handling code Yang Shi
2021-01-28 16:10   ` Vlastimil Babka
2021-01-28 21:16     ` Yang Shi
2021-01-29 14:33   ` Kirill Tkhai
2021-01-29 17:11     ` Yang Shi
2021-01-27 23:33 ` [v5 PATCH 03/11] mm: vmscan: use shrinker_rwsem to protect shrinker_maps allocation Yang Shi
2021-01-28 16:19   ` Vlastimil Babka [this message]
2021-01-27 23:33 ` [v5 PATCH 04/11] mm: vmscan: remove memcg_shrinker_map_size Yang Shi
2021-01-28 16:53   ` Vlastimil Babka
2021-01-28 21:22     ` Yang Shi
2021-01-29 11:22       ` Vlastimil Babka
2021-01-29 17:05         ` Yang Shi
2021-01-27 23:33 ` [v5 PATCH 05/11] mm: memcontrol: rename shrinker_map to shrinker_info Yang Shi
2021-01-28 17:38   ` Vlastimil Babka
2021-01-28 22:05     ` Yang Shi
2021-01-27 23:33 ` [v5 PATCH 06/11] mm: vmscan: use a new flag to indicate shrinker is registered Yang Shi
2021-01-28 17:56   ` Vlastimil Babka
2021-01-28 23:47     ` Yang Shi
2021-01-27 23:33 ` [v5 PATCH 07/11] mm: vmscan: add per memcg shrinker nr_deferred Yang Shi
2021-01-29 13:00   ` Vlastimil Babka
2021-01-29 14:46     ` Kirill Tkhai
2021-01-29 17:20     ` Yang Shi
2021-01-29 18:04       ` Yang Shi
2021-02-01 15:17         ` Vlastimil Babka
2021-02-01 17:09           ` Yang Shi
2021-01-27 23:33 ` [v5 PATCH 08/11] mm: vmscan: use per memcg nr_deferred of shrinker Yang Shi
2021-01-29 14:55   ` Kirill Tkhai
2021-01-29 14:59     ` Kirill Tkhai
2021-01-29 17:22       ` Yang Shi
2021-01-29 15:13   ` Vlastimil Babka
2021-01-29 17:33     ` Yang Shi
2021-01-27 23:33 ` [v5 PATCH 09/11] mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers Yang Shi
2021-01-29 15:40   ` Vlastimil Babka
2021-01-29 17:34     ` Yang Shi
2021-01-27 23:33 ` [v5 PATCH 10/11] mm: memcontrol: reparent nr_deferred when memcg offline Yang Shi
2021-01-29 15:52   ` Vlastimil Babka
2021-01-29 17:38     ` Yang Shi
2021-01-27 23:33 ` [v5 PATCH 11/11] mm: vmscan: shrink deferred objects proportional to priority Yang Shi

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