linux-kernel - Re: [PATCH] Change task

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Date:	Tue, 25 Feb 2014 09:49:40 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
CC:	akpm@...ux-foundation.org, joe@...ches.com, keescook@...omium.org,
	geert@...ux-m68k.org, jkosina@...e.cz, viro@...iv.linux.org.uk,
	davem@...emloft.net, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] Change task_struct->comm to use RCU.

CC scheduler people.

I can't figure out what we get with this patch.

On 02/17/2014 07:27 PM, Tetsuo Handa wrote:
> Tetsuo Handa wrote:
>> This is a draft patch which changes task_struct->comm to use RCU.
> 
> Changes from previous draft version:
> 
>   Changed "struct rcu_comm" to use copy-on-write approach. Those multi-thread
>   or multi-process applications which do not change comm name will consume
>   memory for only one "struct rcu_comm".
> 
>   Changed do_commset() not to sleep.
> 
>   Changed to tolerate loss of consistency when memory allocation failed.
> 
>   Fixed race condition in copy_process().
> 
> Regards.
> ----------
>>>From ada6c4d94f5afda36c7c21869d38b7111a6fe9bc Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Date: Mon, 17 Feb 2014 14:32:11 +0900
> Subject: [PATCH] Change task_struct->comm to use RCU.
> 
> This patch changes task_struct->comm to be updated using RCU
> (unless memory allocation fails).
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> ---
>  fs/exec.c                 |  145 +++++++++++++++++++++++++++++++++++++++------
>  include/linux/init_task.h |    4 +-
>  include/linux/sched.h     |   37 ++++++++++--
>  kernel/fork.c             |    9 +++
>  kernel/kthread.c          |    4 +-
>  kernel/sched/core.c       |    2 +-
>  6 files changed, 173 insertions(+), 28 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index a781dec..8a68ab3 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -263,6 +263,11 @@ extern char ___assert_task_state[1 - 2*!!(
>  
>  /* Task command name length */
>  #define TASK_COMM_LEN 16
> +struct rcu_comm {
> +	char name[TASK_COMM_LEN];
> +	atomic_t usage;
> +	struct rcu_head rcu;
> +};
>  


I think the name "rcu_comm" is not good, I suggest that s/rcu_comm/task_comm/g.

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