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Date:	Fri, 20 Dec 2013 02:26:36 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Tejun Heo <tj@...nel.org>
Cc:	Nigel Cunningham <nigel@...elcunningham.com.au>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Jens Axboe <axboe@...nel.dk>, tomaz.solc@...lix.org,
	aaron.lu@...el.com, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH wq/for-3.14 1/2] workqueue: update max_active clamping rules

On Thursday, December 19, 2013 06:35:26 PM Tejun Heo wrote:
> From bdd220b2a1b86fee14a12b69fb0cadafe60a1dac Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@...nel.org>
> Date: Thu, 19 Dec 2013 18:33:09 -0500
> 
> @max_active handling is currently inconsistent.
> 
> * In alloc_workqueue(), 0 gets converted to the default and the value
>   gets clamped to [1, lim].
> 
> * In workqueue_set_max_active(), 0 is not converted to the default and
>   the value is clamped to [1, lim].
> 
> * When a workqueue is exposed through sysfs, input < 1 fails with
>   -EINVAL; otherwise, the value is clamped to [1, lim].
> 
> * fscache exposes max_active through a sysctl and clamps the value in
>   [1, lim].
> 
> We want to be able to express zero @max_active but as it's a special
> case and 0 is already used for default, don't want to use 0 for it.
> Update @max_active clamping so that the following rules are followed.
> 
> * In both alloc_workqueue() and workqueue_set_max_active(), 0 is
>   converted to the default, and a new special value WQ_FROZEN_ACTIVE
>   becomes 0; otherwise, the value is clamped to [1, lim].
> 
> * In both sysfs and fscache sysctl, input < 1 fails with -EINVAL;
>   otherwise, the value is clamped to [1, lim].
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Lai Jiangshan <laijs@...fujitsu.com>
> Cc: David Howells <dhowells@...hat.com>

Well, this one looks good to me:

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
>  fs/fscache/main.c         | 10 +++++++---
>  include/linux/workqueue.h |  1 +
>  kernel/workqueue.c        |  6 +++++-
>  3 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/fscache/main.c b/fs/fscache/main.c
> index 7c27907..9d5a716 100644
> --- a/fs/fscache/main.c
> +++ b/fs/fscache/main.c
> @@ -62,9 +62,13 @@ static int fscache_max_active_sysctl(struct ctl_table *table, int write,
>  	int ret;
>  
>  	ret = proc_dointvec(table, write, buffer, lenp, ppos);
> -	if (ret == 0)
> -		workqueue_set_max_active(*wqp, *datap);
> -	return ret;
> +	if (ret < 0)
> +		return ret;
> +	if (*datap < 1)
> +		return -EINVAL;
> +
> +	workqueue_set_max_active(*wqp, *datap);
> +	return 0;
>  }
>  
>  ctl_table fscache_sysctls[] = {
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index 594521b..334daa3 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -338,6 +338,7 @@ enum {
>  	__WQ_DRAINING		= 1 << 16, /* internal: workqueue is draining */
>  	__WQ_ORDERED		= 1 << 17, /* internal: workqueue is ordered */
>  
> +	WQ_FROZEN_ACTIVE	= -1,	  /* special value for frozen wq */
>  	WQ_MAX_ACTIVE		= 512,	  /* I like 512, better ideas? */
>  	WQ_MAX_UNBOUND_PER_CPU	= 4,	  /* 4 * #cpus for unbound wq */
>  	WQ_DFL_ACTIVE		= WQ_MAX_ACTIVE / 2,
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 987293d..6748fbf 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -4136,6 +4136,11 @@ static int wq_clamp_max_active(int max_active, unsigned int flags,
>  {
>  	int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;
>  
> +	if (max_active == 0)
> +		return WQ_DFL_ACTIVE;
> +	if (max_active == WQ_FROZEN_ACTIVE)
> +		return 0;
> +
>  	if (max_active < 1 || max_active > lim)
>  		pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
>  			max_active, name, 1, lim);
> @@ -4176,7 +4181,6 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
>  	vsnprintf(wq->name, sizeof(wq->name), fmt, args);
>  	va_end(args);
>  
> -	max_active = max_active ?: WQ_DFL_ACTIVE;
>  	max_active = wq_clamp_max_active(max_active, flags, wq->name);
>  
>  	/* init wq */
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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