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From: Andrew Morton <akpm@linux-foundation.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: kamezawa.hiroyu@jp.fujitsu.com, nishimura@mxp.nes.nec.co.jp,
	balbir@linux.vnet.ibm.com, minchan.kim@gmail.com,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [patch 2/3] memcg: prevent endless loop when charging huge pages to near-limit group
Date: Mon, 31 Jan 2011 14:41:31 -0800	[thread overview]
Message-ID: <20110131144131.6733aa3a.akpm@linux-foundation.org> (raw)
In-Reply-To: <1296482635-13421-3-git-send-email-hannes@cmpxchg.org>

On Mon, 31 Jan 2011 15:03:54 +0100
Johannes Weiner <hannes@cmpxchg.org> wrote:

> +static inline bool res_counter_check_margin(struct res_counter *cnt,
> +					    unsigned long bytes)
> +{
> +	bool ret;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&cnt->lock, flags);
> +	ret = cnt->limit - cnt->usage >= bytes;
> +	spin_unlock_irqrestore(&cnt->lock, flags);
> +	return ret;
> +}
> +
>  static inline bool res_counter_check_under_soft_limit(struct res_counter *cnt)
>  {
>  	bool ret;
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 73ea323..c28072f 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1111,6 +1111,15 @@ static bool mem_cgroup_check_under_limit(struct mem_cgroup *mem)
>  	return false;
>  }
>  
> +static bool mem_cgroup_check_margin(struct mem_cgroup *mem, unsigned long bytes)
> +{
> +	if (!res_counter_check_margin(&mem->res, bytes))
> +		return false;
> +	if (do_swap_account && !res_counter_check_margin(&mem->memsw, bytes))
> +		return false;
> +	return true;
> +}

argh.

If you ever have a function with the string "check" in its name, it's a
good sign that you did something wrong.

Check what?  Against what?  Returning what?

mem_cgroup_check_under_limit() isn't toooo bad - the name tells you
what's being checked and tells you what to expect the return value to
mean.

But "res_counter_check_margin" and "mem_cgroup_check_margin" are just
awful.  Something like

	bool res_counter_may_charge(counter, bytes)

would be much clearer.

If we really want to stick with the "check" names (perhaps as an ironic
reference to res_counter's past mistakes) then please at least document
the sorry things?


  reply	other threads:[~2011-01-31 22:42 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-31 14:03 Johannes Weiner
2011-01-31 14:03 ` [patch 1/3] memcg: prevent endless loop when charging huge pages Johannes Weiner
2011-01-31 22:27   ` Minchan Kim
2011-01-31 23:48   ` KAMEZAWA Hiroyuki
2011-01-31 14:03 ` [patch 2/3] memcg: prevent endless loop when charging huge pages to near-limit group Johannes Weiner
2011-01-31 22:41   ` Andrew Morton [this message]
2011-01-31 23:50     ` KAMEZAWA Hiroyuki
2011-02-01  0:04     ` Johannes Weiner
2011-02-01  0:24       ` Andrew Morton
2011-02-01  0:34         ` Johannes Weiner
2011-02-03 12:53         ` [patch 0/2] memcg: clean up limit checking Johannes Weiner
2011-02-03 12:54           ` [patch 1/2] memcg: soft limit reclaim should end at limit not below Johannes Weiner
2011-02-03 23:41             ` KAMEZAWA Hiroyuki
2011-02-04  4:10             ` Balbir Singh
2011-02-03 12:56           ` [patch 2/2] memcg: simplify the way memory limits are checked Johannes Weiner
2011-02-03 23:44             ` KAMEZAWA Hiroyuki
2011-02-04  4:12             ` Balbir Singh
2011-01-31 22:42   ` [patch 2/3] memcg: prevent endless loop when charging huge pages to near-limit group Minchan Kim
2011-01-31 14:03 ` [patch 3/3] memcg: never OOM when charging huge pages Johannes Weiner
2011-01-31 22:52   ` Minchan Kim
2011-01-31 23:51   ` KAMEZAWA Hiroyuki

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