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Thu, 23 Feb 2023 05:28:00 -0800 (PST) From: Qi Zheng To: 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 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, Qi Zheng Subject: [PATCH v2 2/7] mm: vmscan: make global slab shrink lockless Date: Thu, 23 Feb 2023 21:27:20 +0800 Message-Id: <20230223132725.11685-3-zhengqi.arch@bytedance.com> X-Mailer: git-send-email 2.24.3 (Apple Git-128) In-Reply-To: <20230223132725.11685-1-zhengqi.arch@bytedance.com> References: <20230223132725.11685-1-zhengqi.arch@bytedance.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 5001720012 X-Rspam-User: X-Stat-Signature: 68j5rayyw6de6jewk3nggwsxnfp3sfpg X-HE-Tag: 1677158882-49375 X-HE-Meta: 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 UYqURBFs 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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: 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); - list_add_tail(&shrinker->list, &shrinker_list); + list_add_tail_rcu(&shrinker->list, &shrinker_list); shrinker->flags |= SHRINKER_REGISTERED; shrinker_debugfs_add(shrinker); up_write(&shrinker_rwsem); @@ -760,13 +761,15 @@ void unregister_shrinker(struct shrinker *shrinker) return; down_write(&shrinker_rwsem); - list_del(&shrinker->list); + list_del_rcu(&shrinker->list); shrinker->flags &= ~SHRINKER_REGISTERED; if (shrinker->flags & SHRINKER_MEMCG_AWARE) unregister_memcg_shrinker(shrinker); debugfs_entry = shrinker_debugfs_remove(shrinker); up_write(&shrinker_rwsem); + synchronize_srcu(&shrinker_srcu); + debugfs_remove_recursive(debugfs_entry); kfree(shrinker->nr_deferred); @@ -786,6 +789,7 @@ void synchronize_shrinkers(void) { down_write(&shrinker_rwsem); up_write(&shrinker_rwsem); + synchronize_srcu(&shrinker_srcu); } EXPORT_SYMBOL(synchronize_shrinkers); @@ -996,6 +1000,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, { unsigned long ret, freed = 0; struct shrinker *shrinker; + int srcu_idx; /* * The root memcg might be allocated even though memcg is disabled @@ -1007,10 +1012,10 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) return shrink_slab_memcg(gfp_mask, nid, memcg, priority); - if (!down_read_trylock(&shrinker_rwsem)) - goto out; + srcu_idx = srcu_read_lock(&shrinker_srcu); - list_for_each_entry(shrinker, &shrinker_list, list) { + list_for_each_entry_srcu(shrinker, &shrinker_list, list, + srcu_read_lock_held(&shrinker_srcu)) { struct shrink_control sc = { .gfp_mask = gfp_mask, .nid = nid, @@ -1021,19 +1026,9 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, if (ret == SHRINK_EMPTY) ret = 0; freed += ret; - /* - * Bail out if someone want to register a new shrinker to - * prevent the registration from being stalled for long periods - * by parallel ongoing shrinking. - */ - if (rwsem_is_contended(&shrinker_rwsem)) { - freed = freed ? : 1; - break; - } } - up_read(&shrinker_rwsem); -out: + srcu_read_unlock(&shrinker_srcu, srcu_idx); cond_resched(); return freed; } -- 2.20.1