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From: Michal Hocko <mhocko@suse.cz>
To: Glauber Costa <glommer@parallels.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Mel Gorman <mgorman@suse.de>,
	Suleiman Souhlal <suleiman@google.com>, Tejun Heo <tj@kernel.org>,
	cgroups@vger.kernel.org, kamezawa.hiroyu@jp.fujitsu.com,
	Johannes Weiner <hannes@cmpxchg.org>,
	Greg Thelen <gthelen@google.com>,
	devel@openvz.org, Frederic Weisbecker <fweisbec@gmail.com>,
	Christoph Lameter <cl@linux.com>,
	Pekka Enberg <penberg@cs.helsinki.fi>
Subject: Re: [PATCH v4 09/14] memcg: kmem accounting lifecycle management
Date: Thu, 11 Oct 2012 15:11:43 +0200	[thread overview]
Message-ID: <20121011131143.GF29295@dhcp22.suse.cz> (raw)
In-Reply-To: <1349690780-15988-10-git-send-email-glommer@parallels.com>

On Mon 08-10-12 14:06:15, Glauber Costa wrote:
> Because kmem charges can outlive the cgroup, we need to make sure that
> we won't free the memcg structure while charges are still in flight.
> For reviewing simplicity, the charge functions will issue
> mem_cgroup_get() at every charge, and mem_cgroup_put() at every
> uncharge.
> 
> This can get expensive, however, and we can do better. mem_cgroup_get()
> only really needs to be issued once: when the first limit is set. In the
> same spirit, we only need to issue mem_cgroup_put() when the last charge
> is gone.
> 
> We'll need an extra bit in kmem_accounted for that: KMEM_ACCOUNTED_DEAD.
> it will be set when the cgroup dies, if there are charges in the group.
> If there aren't, we can proceed right away.
> 
> Our uncharge function will have to test that bit every time the charges
> drop to 0. Because that is not the likely output of
> res_counter_uncharge, this should not impose a big hit on us: it is
> certainly much better than a reference count decrease at every
> operation.
> 
> [ v3: merged all lifecycle related patches in one ]
> 
> Signed-off-by: Glauber Costa <glommer@parallels.com>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> CC: Christoph Lameter <cl@linux.com>
> CC: Pekka Enberg <penberg@cs.helsinki.fi>
> CC: Michal Hocko <mhocko@suse.cz>
> CC: Johannes Weiner <hannes@cmpxchg.org>
> CC: Suleiman Souhlal <suleiman@google.com>

OK, I like the optimization. I have just one comment to the
memcg_kmem_dead naming but other than that

Acked-by: Michal Hocko <mhocko@suse.cz>

[...]
> +static bool memcg_kmem_dead(struct mem_cgroup *memcg)

The name is tricky because it doesn't tell you that it clears the flag
which made me scratch my head when reading comment in kmem_cgroup_destroy

> +{
> +	return test_and_clear_bit(KMEM_ACCOUNTED_DEAD, &memcg->kmem_accounted);
> +}
>  #endif
>  
>  /* Stuffs for move charges at task migration. */
[...]
> @@ -4876,6 +4904,20 @@ static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
>  static void kmem_cgroup_destroy(struct mem_cgroup *memcg)
>  {
>  	mem_cgroup_sockets_destroy(memcg);
> +
> +	memcg_kmem_mark_dead(memcg);
> +
> +	if (res_counter_read_u64(&memcg->kmem, RES_USAGE) != 0)
> +		return;
> +
> +	/*
> +	 * Charges already down to 0, undo mem_cgroup_get() done in the charge
> +	 * path here, being careful not to race with memcg_uncharge_kmem: it is
> +	 * possible that the charges went down to 0 between mark_dead and the
> +	 * res_counter read, so in that case, we don't need the put
> +	 */
> +	if (memcg_kmem_dead(memcg))
> +		mem_cgroup_put(memcg);

-- 
Michal Hocko
SUSE Labs

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  reply	other threads:[~2012-10-11 13:11 UTC|newest]

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-10-08 10:06 [PATCH v4 00/14] kmem controller for memcg Glauber Costa
2012-10-08 10:06 ` [PATCH v4 01/14] memcg: Make it possible to use the stock for more than one page Glauber Costa
2012-10-08 10:06 ` [PATCH v4 02/14] memcg: Reclaim when more than one page needed Glauber Costa
2012-10-16  3:22   ` Kamezawa Hiroyuki
2012-10-08 10:06 ` [PATCH v4 03/14] memcg: change defines to an enum Glauber Costa
2012-10-08 10:06 ` [PATCH v4 04/14] kmem accounting basic infrastructure Glauber Costa
2012-10-11 10:11   ` Michal Hocko
2012-10-11 12:53     ` Michal Hocko
2012-10-11 13:38     ` Michal Hocko
2012-10-12  7:36     ` Glauber Costa
2012-10-12  8:27       ` Michal Hocko
2012-10-08 10:06 ` [PATCH v4 05/14] Add a __GFP_KMEMCG flag Glauber Costa
2012-10-09 15:04   ` Michal Hocko
2012-10-08 10:06 ` [PATCH v4 06/14] memcg: kmem controller infrastructure Glauber Costa
2012-10-11 12:42   ` Michal Hocko
2012-10-11 12:56     ` Michal Hocko
2012-10-12  7:45     ` Glauber Costa
2012-10-12  8:39       ` Michal Hocko
2012-10-12  8:44         ` Glauber Costa
2012-10-12  8:57           ` Michal Hocko
2012-10-12  9:13             ` Glauber Costa
2012-10-12  9:47               ` Michal Hocko
2012-10-16  8:00               ` Kamezawa Hiroyuki
2012-10-08 10:06 ` [PATCH v4 07/14] mm: Allocate kernel pages to the right memcg Glauber Costa
2012-10-08 10:06 ` [PATCH v4 08/14] res_counter: return amount of charges after res_counter_uncharge Glauber Costa
2012-10-09 15:08   ` Michal Hocko
2012-10-09 15:14     ` Glauber Costa
2012-10-09 15:35       ` Michal Hocko
2012-10-10  9:03         ` Glauber Costa
2012-10-10 11:24           ` Michal Hocko
2012-10-10 11:25   ` Michal Hocko
2012-10-16  8:20   ` Kamezawa Hiroyuki
2012-10-08 10:06 ` [PATCH v4 09/14] memcg: kmem accounting lifecycle management Glauber Costa
2012-10-11 13:11   ` Michal Hocko [this message]
2012-10-12  7:47     ` Glauber Costa
2012-10-12  8:41       ` Michal Hocko
2012-10-16  8:41         ` Kamezawa Hiroyuki
2012-10-08 10:06 ` [PATCH v4 10/14] memcg: use static branches when code not in use Glauber Costa
2012-10-11 13:40   ` Michal Hocko
2012-10-12  7:47     ` Glauber Costa
2012-10-16  8:48       ` Kamezawa Hiroyuki
2012-10-08 10:06 ` [PATCH v4 11/14] memcg: allow a memcg with kmem charges to be destructed Glauber Costa
2012-10-08 10:06 ` [PATCH v4 12/14] execute the whole memcg freeing in free_worker Glauber Costa
2012-10-11 14:21   ` Michal Hocko
2012-10-08 10:06 ` [PATCH v4 13/14] protect architectures where THREAD_SIZE >= PAGE_SIZE against fork bombs Glauber Costa
2012-10-08 10:06 ` [PATCH v4 14/14] Add documentation about the kmem controller Glauber Costa
2012-10-11 14:35   ` Michal Hocko
2012-10-12  7:53     ` Glauber Costa
2012-10-12  8:44       ` Michal Hocko
2012-10-17  7:29   ` Kamezawa Hiroyuki

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