linux-kernel - Re: [PATCH v2 19/29] skip memcg kmem allocations in specified code regions

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Message-ID: <4FB1C398.1010000@jp.fujitsu.com>
Date:	Tue, 15 May 2012 11:46:48 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.com>
CC:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, Tejun Heo <tj@...nel.org>,
	Li Zefan <lizefan@...wei.com>,
	Greg Thelen <gthelen@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>, devel@...nvz.org,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v2 19/29] skip memcg kmem allocations in specified code
 regions

(2012/05/12 2:44), Glauber Costa wrote:

> This patch creates a mechanism that skip memcg allocations during
> certain pieces of our core code. It basically works in the same way
> as preempt_disable()/preempt_enable(): By marking a region under
> which all allocations will be accounted to the root memcg.
> 
> We need this to prevent races in early cache creation, when we
> allocate data using caches that are not necessarily created already.
> 
> Signed-off-by: Glauber Costa <glommer@...allels.com>
> CC: Christoph Lameter <cl@...ux.com>
> CC: Pekka Enberg <penberg@...helsinki.fi>
> CC: Michal Hocko <mhocko@...e.cz>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> CC: Johannes Weiner <hannes@...xchg.org>
> CC: Suleiman Souhlal <suleiman@...gle.com>


The concept seems okay to me but...

> ---
>  include/linux/sched.h |    1 +
>  mm/memcontrol.c       |   25 +++++++++++++++++++++++++
>  2 files changed, 26 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 81a173c..0501114 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1613,6 +1613,7 @@ struct task_struct {
>  		unsigned long nr_pages;	/* uncharged usage */
>  		unsigned long memsw_nr_pages; /* uncharged mem+swap usage */
>  	} memcg_batch;
> +	atomic_t memcg_kmem_skip_account;


If only 'current' thread touch this, you don't need to make this atomic counter.
you can use 'long'.

Thanks,
-Kame

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