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Thu, 23 Feb 2023 20:10:00 -0800 (PST) Received: from [10.70.252.135] ([139.177.225.245]) by smtp.gmail.com with ESMTPSA id q15-20020a62ae0f000000b005a9131b6668sm2815781pff.2.2023.02.23.20.09.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Feb 2023 20:09:59 -0800 (PST) Message-ID: <684fab83-a506-33fc-4b24-bdf0902e2397@bytedance.com> Date: Fri, 24 Feb 2023 12:09:52 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.7.2 Subject: Re: [PATCH v2 2/7] mm: vmscan: make global slab shrink lockless Content-Language: en-US To: Rafael Aquini Cc: akpm@linux-foundation.org, tkhai@ya.ru, hannes@cmpxchg.org, shakeelb@google.com, mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev, david@redhat.com, shy828301@gmail.com, 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: <20230223132725.11685-1-zhengqi.arch@bytedance.com> <20230223132725.11685-3-zhengqi.arch@bytedance.com> From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6E9C716001A X-Stat-Signature: 6j4hxcmroxqbdu74joga4taxb7rkyuwz X-HE-Tag: 1677211801-172058 X-HE-Meta: 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 sQwNoVzF 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2023/2/23 23:37, Rafael Aquini wrote: > On Thu, Feb 23, 2023 at 10:26:45AM -0500, Rafael Aquini wrote: >> On Thu, Feb 23, 2023 at 09:27:20PM +0800, Qi Zheng wrote: >>> The shrinker_rwsem is a global lock in shrinkers subsystem, >>> it is easy to cause blocking in the following cases: >>> >>> a. the write lock of shrinker_rwsem was held for too long. >>> For example, there are many memcgs in the system, which >>> causes some paths to hold locks and traverse it for too >>> long. (e.g. expand_shrinker_info()) >>> b. the read lock of shrinker_rwsem was held for too long, >>> and a writer came at this time. Then this writer will be >>> forced to wait and block all subsequent readers. >>> For example: >>> - be scheduled when the read lock of shrinker_rwsem is >>> held in do_shrink_slab() >>> - some shrinker are blocked for too long. Like the case >>> mentioned in the patchset[1]. >>> >>> Therefore, many times in history ([2],[3],[4],[5]), some >>> people wanted to replace shrinker_rwsem reader with SRCU, >>> but they all gave up because SRCU was not unconditionally >>> enabled. >>> >>> But now, since commit 1cd0bd06093c ("rcu: Remove CONFIG_SRCU"), >>> the SRCU is unconditionally enabled. So it's time to use >>> SRCU to protect readers who previously held shrinker_rwsem. >>> >>> [1]. https://lore.kernel.org/lkml/20191129214541.3110-1-ptikhomirov@virtuozzo.com/ >>> [2]. https://lore.kernel.org/all/1437080113.3596.2.camel@stgolabs.net/ >>> [3]. https://lore.kernel.org/lkml/1510609063-3327-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp/ >>> [4]. https://lore.kernel.org/lkml/153365347929.19074.12509495712735843805.stgit@localhost.localdomain/ >>> [5]. https://lore.kernel.org/lkml/20210927074823.5825-1-sultan@kerneltoast.com/ >>> >>> Signed-off-by: Qi Zheng >>> --- >>> mm/vmscan.c | 27 +++++++++++---------------- >>> 1 file changed, 11 insertions(+), 16 deletions(-) >>> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index 9f895ca6216c..02987a6f95d1 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -202,6 +202,7 @@ static void set_task_reclaim_state(struct task_struct *task, >>> >>> LIST_HEAD(shrinker_list); >>> DECLARE_RWSEM(shrinker_rwsem); >>> +DEFINE_SRCU(shrinker_srcu); >>> >>> #ifdef CONFIG_MEMCG >>> static int shrinker_nr_max; >>> @@ -706,7 +707,7 @@ void free_prealloced_shrinker(struct shrinker *shrinker) >>> void register_shrinker_prepared(struct shrinker *shrinker) >>> { >>> down_write(&shrinker_rwsem); >> >> I think you could revert the rwsem back to a simple mutex, now. >> > > NVM, that's exactly what patch 7 does. :) Yeah. :) > > > -- Thanks, Qi