From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: apolyakov@beget.ru, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, ktkhai@virtuozzo.com, vdavydov.dev@gmail.com,
aryabinin@virtuozzo.com, akpm@linux-foundation.org
Subject: [PATCH 3/3] mm: Count list_lru_one::nr_items lockless
Date: Tue, 22 Aug 2017 15:29:35 +0300 [thread overview]
Message-ID: <150340497499.3845.3045559119569209195.stgit@localhost.localdomain> (raw)
In-Reply-To: <150340381428.3845.6099251634440472539.stgit@localhost.localdomain>
During the reclaiming slab of a memcg, shrink_slab iterates
over all registered shrinkers in the system, and tries to count
and consume objects related to the cgroup. In case of memory
pressure, this behaves bad: I observe high system time and
time spent in list_lru_count_one() for many processes on RHEL7
kernel (collected via $perf record --call-graph fp -j k -a):
0,50% nixstatsagent [kernel.vmlinux] [k] _raw_spin_lock [k] _raw_spin_lock
0,26% nixstatsagent [kernel.vmlinux] [k] shrink_slab [k] shrink_slab
0,23% nixstatsagent [kernel.vmlinux] [k] super_cache_count [k] super_cache_count
0,15% nixstatsagent [kernel.vmlinux] [k] __list_lru_count_one.isra.2 [k] _raw_spin_lock
0,15% nixstatsagent [kernel.vmlinux] [k] list_lru_count_one [k] __list_lru_count_one.isra.2
0,94% mysqld [kernel.vmlinux] [k] _raw_spin_lock [k] _raw_spin_lock
0,57% mysqld [kernel.vmlinux] [k] shrink_slab [k] shrink_slab
0,51% mysqld [kernel.vmlinux] [k] super_cache_count [k] super_cache_count
0,32% mysqld [kernel.vmlinux] [k] __list_lru_count_one.isra.2 [k] _raw_spin_lock
0,32% mysqld [kernel.vmlinux] [k] list_lru_count_one [k] __list_lru_count_one.isra.2
0,73% sshd [kernel.vmlinux] [k] _raw_spin_lock [k] _raw_spin_lock
0,35% sshd [kernel.vmlinux] [k] shrink_slab [k] shrink_slab
0,32% sshd [kernel.vmlinux] [k] super_cache_count [k] super_cache_count
0,21% sshd [kernel.vmlinux] [k] __list_lru_count_one.isra.2 [k] _raw_spin_lock
0,21% sshd [kernel.vmlinux] [k] list_lru_count_one [k] __list_lru_count_one.isra.2
This patch aims to make super_cache_count() more effective. It
makes __list_lru_count_one() count nr_items lockless to minimize
overhead introducing by locking operation, and to make parallel
reclaims more scalable.
The lock won't be taken on shrinker::count_objects(),
it would be taken only for the real shrink by the thread,
who realizes it.
https://jira.sw.ru/browse/PSBM-69296
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
mm/list_lru.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/list_lru.c b/mm/list_lru.c
index 2db3cdadb577..8d1d2db5f4fb 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -177,10 +177,10 @@ static unsigned long __list_lru_count_one(struct list_lru *lru,
struct list_lru_one *l;
unsigned long count;
- spin_lock(&nlru->lock);
+ rcu_read_lock();
l = list_lru_from_memcg_idx(nlru, memcg_idx);
count = l->nr_items;
- spin_unlock(&nlru->lock);
+ rcu_read_unlock();
return count;
}
--
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next prev parent reply other threads:[~2017-08-22 12:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-22 12:29 [PATCH 0/3] Make count list_lru_one::nr_items lockless Kirill Tkhai
2017-08-22 12:29 ` [PATCH 1/3] mm: Add rcu field to struct list_lru_memcg Kirill Tkhai
2017-08-22 12:29 ` [PATCH 2/3] mm: Make list_lru_node::memcg_lrus RCU protected Kirill Tkhai
2017-08-22 19:34 ` Vladimir Davydov
2017-08-22 12:29 ` Kirill Tkhai [this message]
2017-08-22 19:47 ` [PATCH 3/3] mm: Count list_lru_one::nr_items lockless Vladimir Davydov
2017-08-23 8:00 ` Kirill Tkhai
2017-08-23 8:27 ` Vladimir Davydov
2017-08-23 12:26 ` Kirill Tkhai
2017-08-26 17:57 ` Vladimir Davydov
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