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[73.249.122.233]) by smtp.gmail.com with ESMTPSA id dw16-20020a05620a601000b0073bad2f9380sm3042966qkb.14.2023.02.23.07.37.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Feb 2023 07:37:23 -0800 (PST) Date: Thu, 23 Feb 2023 10:37:21 -0500 From: Rafael Aquini To: Qi Zheng 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 Subject: Re: [PATCH v2 2/7] mm: vmscan: make global slab shrink lockless Message-ID: References: <20230223132725.11685-1-zhengqi.arch@bytedance.com> <20230223132725.11685-3-zhengqi.arch@bytedance.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: B7E254001B X-Rspam-User: X-Stat-Signature: czfdq74fiwmnb5icywpjoitwg6nur5c9 X-HE-Tag: 1677166646-128181 X-HE-Meta: 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 Hg4ZTqUh 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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 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. :)