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From: Vladimir Davydov <>
To: Kirill Tkhai <>
Subject: Re: [PATCH 3/3] mm: Count list_lru_one::nr_items lockless
Date: Tue, 22 Aug 2017 22:47:25 +0300	[thread overview]
Message-ID: <20170822194725.ik3xwxu67wcthisb@esperanza> (raw)
In-Reply-To: <150340497499.3845.3045559119569209195.stgit@localhost.localdomain>

On Tue, Aug 22, 2017 at 03:29:35PM +0300, Kirill Tkhai wrote:
> 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

It would be nice to see how this is improved by this patch.
Can you try to record the traces on the vanilla kernel with
and without this patch?

> 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.


Not relevant.

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  reply	other threads:[~2017-08-22 19:47 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 ` [PATCH 3/3] mm: Count list_lru_one::nr_items lockless Kirill Tkhai
2017-08-22 19:47   ` Vladimir Davydov [this message]
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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