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Sun, 26 Feb 2023 06:48:21 -0800 (PST) Received: from localhost.localdomain ([139.177.225.248]) by smtp.gmail.com with ESMTPSA id y20-20020a170902ed5400b0019c2cf12d15sm2755589plb.116.2023.02.26.06.48.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 26 Feb 2023 06:48:21 -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 v3 2/8] mm: vmscan: make global slab shrink lockless Date: Sun, 26 Feb 2023 22:46:49 +0800 Message-Id: <20230226144655.79778-3-zhengqi.arch@bytedance.com> X-Mailer: git-send-email 2.24.3 (Apple Git-128) In-Reply-To: <20230226144655.79778-1-zhengqi.arch@bytedance.com> References: <20230226144655.79778-1-zhengqi.arch@bytedance.com> MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4E8924001A X-Stat-Signature: owrgpr1xhyin16iod6wow8fgx4amfymr X-HE-Tag: 1677422903-117693 X-HE-Meta: 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 811m5ojl 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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 546c07ccb3bc..2a21a84d3db1 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; }