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From: Andrew Morton <akpm@linux-foundation.org>
To: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: vdavydov.dev@gmail.com, apolyakov@beget.ru,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	aryabinin@virtuozzo.com
Subject: Re: [PATCH] mm: Make count list_lru_one::nr_items lockless
Date: Thu, 28 Sep 2017 14:02:30 -0700	[thread overview]
Message-ID: <20170928140230.a9a0cd44a09eae9441a83bdc@linux-foundation.org> (raw)
In-Reply-To: <fbb67bef-c13f-7fcb-fa6a-e3a7f6e5c82b@virtuozzo.com>

On Thu, 28 Sep 2017 10:48:55 +0300 Kirill Tkhai <ktkhai@virtuozzo.com> wrote:

> >> This patch aims to make super_cache_count() (and other functions,
> >> which count LRU nr_items) more effective.
> >> It allows list_lru_node::memcg_lrus to be RCU-accessed, and makes
> >> __list_lru_count_one() count nr_items lockless to minimize
> >> overhead introduced by locking operation, and to make parallel
> >> reclaims more scalable.
> > 
> > And...  what were the effects of the patch?  Did you not run the same
> > performance tests after applying it?
> 
> I've just detected the such high usage of shrink slab on production node. It's rather
> difficult to make it use another kernel, than it uses, only kpatches are possible.
> So, I haven't estimated how it acts on node's performance.
> On test node I see, that the patch obviously removes raw_spin_lock from perf profile.
> So, it's a little bit untested in this way.

Well that's a problem.  The patch increases list_lru.o text size by a
lot (4800->5696) which will have a cost.  And we don't have proof that
any benefit is worth that cost.  It shouldn't be too hard to cook up a
synthetic test to trigger memcg slab reclaim and then run a
before-n-after benchmark?

WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: vdavydov.dev@gmail.com, apolyakov@beget.ru,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	aryabinin@virtuozzo.com
Subject: Re: [PATCH] mm: Make count list_lru_one::nr_items lockless
Date: Thu, 28 Sep 2017 14:02:30 -0700	[thread overview]
Message-ID: <20170928140230.a9a0cd44a09eae9441a83bdc@linux-foundation.org> (raw)
In-Reply-To: <fbb67bef-c13f-7fcb-fa6a-e3a7f6e5c82b@virtuozzo.com>

On Thu, 28 Sep 2017 10:48:55 +0300 Kirill Tkhai <ktkhai@virtuozzo.com> wrote:

> >> This patch aims to make super_cache_count() (and other functions,
> >> which count LRU nr_items) more effective.
> >> It allows list_lru_node::memcg_lrus to be RCU-accessed, and makes
> >> __list_lru_count_one() count nr_items lockless to minimize
> >> overhead introduced by locking operation, and to make parallel
> >> reclaims more scalable.
> > 
> > And...  what were the effects of the patch?  Did you not run the same
> > performance tests after applying it?
> 
> I've just detected the such high usage of shrink slab on production node. It's rather
> difficult to make it use another kernel, than it uses, only kpatches are possible.
> So, I haven't estimated how it acts on node's performance.
> On test node I see, that the patch obviously removes raw_spin_lock from perf profile.
> So, it's a little bit untested in this way.

Well that's a problem.  The patch increases list_lru.o text size by a
lot (4800->5696) which will have a cost.  And we don't have proof that
any benefit is worth that cost.  It shouldn't be too hard to cook up a
synthetic test to trigger memcg slab reclaim and then run a
before-n-after benchmark?

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  reply	other threads:[~2017-09-28 21:02 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-19 15:06 [PATCH] mm: Make count list_lru_one::nr_items lockless Kirill Tkhai
2017-09-19 15:06 ` Kirill Tkhai
2017-09-27 21:15 ` Andrew Morton
2017-09-27 21:15   ` Andrew Morton
2017-09-28  7:48   ` Kirill Tkhai
2017-09-28  7:48     ` Kirill Tkhai
2017-09-28 21:02     ` Andrew Morton [this message]
2017-09-28 21:02       ` Andrew Morton
2017-09-29  8:15       ` Kirill Tkhai
2017-09-29  8:15         ` Kirill Tkhai
2017-11-30  0:27         ` Shakeel Butt
2017-11-30  0:27           ` Shakeel Butt
2017-11-30 10:36           ` Kirill Tkhai
2017-11-30 10:36             ` Kirill Tkhai

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