lkml.org 
[lkml]   [2017]   [Aug]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Subject[PATCH 3/3] mm: Count list_lru_one::nr_items lockless
From
Date
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;
}
\
 
 \ /
  Last update: 2017-08-22 14:30    [W:0.072 / U:0.896 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site