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From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: apolyakov@beget.ru, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, aryabinin@virtuozzo.com,
	akpm@linux-foundation.org
Subject: Re: [PATCH 3/3] mm: Count list_lru_one::nr_items lockless
Date: Wed, 23 Aug 2017 11:00:56 +0300	[thread overview]
Message-ID: <b1600bca-32cc-e285-8589-778999584d5a@virtuozzo.com> (raw)
In-Reply-To: <20170822194725.ik3xwxu67wcthisb@esperanza>

On 22.08.2017 22:47, Vladimir Davydov wrote:
> 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?

Sadly, the talk is about a production node, and it's impossible to use vanila kernel there.

>>
>> 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
> 
> Not relevant.
> 

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  reply	other threads:[~2017-08-23  8:01 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
2017-08-23  8:00     ` Kirill Tkhai [this message]
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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