linux-kernel - Re: [PATCH 8/8] res_counter: Allow charge failure pointer to be null

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Date:	Wed, 17 Aug 2011 10:44:22 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Menage <menage@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Aditya Kali <adityakali@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 8/8] res_counter: Allow charge failure pointer to be null

Frederic Weisbecker wrote:
> So that callers of res_counter_charge() don't have to create and
> pass this pointer even if they aren't interested in it.
> 

Why not make this change early, or even do this in "[PATCH 5/8]".

> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Paul Menage <menage@...gle.com>
> Cc: Li Zefan <lizf@...fujitsu.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Aditya Kali <adityakali@...gle.com>
> Cc: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/cgroup_task_counter.c |    6 ++----
>  kernel/res_counter.c         |    6 ++++--
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/cgroup_task_counter.c b/kernel/cgroup_task_counter.c
> index 7f12ac9..dacc4a9 100644
> --- a/kernel/cgroup_task_counter.c
> +++ b/kernel/cgroup_task_counter.c
> @@ -93,11 +93,10 @@ static int task_counter_can_attach_task(struct cgroup *cgrp, struct cgroup *old_
>  {
>  	struct res_counter *res = cgroup_task_counter_res(cgrp);
>  	struct res_counter *old_res = cgroup_task_counter_res(old_cgrp);
> -	struct res_counter *limit_fail_at;
>  
>  	common_ancestor = res_counter_common_ancestor(res, old_res);
>  
> -	return res_counter_charge_until(res, common_ancestor, 1, &limit_fail_at);
> +	return res_counter_charge_until(res, common_ancestor, 1, NULL);
>  }
>  
>  static void task_counter_cancel_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
> @@ -154,13 +153,12 @@ int cgroup_task_counter_fork(struct task_struct *child)
>  {
>  	struct cgroup_subsys_state *css = child->cgroups->subsys[tasks_subsys_id];
>  	struct cgroup *cgrp = css->cgroup;
> -	struct res_counter *limit_fail_at;
>  
>  	/* Optimize for the root cgroup case, which doesn't have a limit */
>  	if (!cgrp->parent)
>  		return 0;
>  
> -	return res_counter_charge(cgroup_task_counter_res(cgrp), 1, &limit_fail_at);
> +	return res_counter_charge(cgroup_task_counter_res(cgrp), 1, NULL);
>  }
>  
>  struct cgroup_subsys tasks_subsys = {
> diff --git a/kernel/res_counter.c b/kernel/res_counter.c
> index 725dfa6..7eac803 100644
> --- a/kernel/res_counter.c
> +++ b/kernel/res_counter.c
> @@ -43,14 +43,16 @@ int res_counter_charge_until(struct res_counter *counter,
>  	unsigned long flags;
>  	struct res_counter *c, *u;
>  
> -	*limit_fail_at = NULL;
> +	if (limit_fail_at)
> +		*limit_fail_at = NULL;
>  	local_irq_save(flags);
>  	for (c = counter; c != limit; c = c->parent) {
>  		spin_lock(&c->lock);
>  		ret = res_counter_charge_locked(c, val);
>  		spin_unlock(&c->lock);
>  		if (ret < 0) {
> -			*limit_fail_at = c;
> +			if (limit_fail_at)
> +				*limit_fail_at = c;
>  			goto undo;
>  		}
>  	}
--
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