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Date: Tue, 19 Jul 2016 15:07:08 -0400
From: Tejun Heo <tj@kernel.org>
To: Topi Miettinen <toiwoton@gmail.com>
Cc: linux-kernel@vger.kernel.org, Li Zefan <lizefan@huawei.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@vger.kernel.org>
Subject: Re: [PATCH 1/2] cgroup_pids: track highwater mark of pids
Message-ID: <20160719190708.GO3078@mtj.duckdns.org>
References: <1468785820-3960-1-git-send-email-toiwoton@gmail.com>
 <1468785820-3960-3-git-send-email-toiwoton@gmail.com>
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Hello,

On Sun, Jul 17, 2016 at 11:03:38PM +0300, Topi Miettinen wrote:
> +static void pids_update_highwater_mark(struct pids_cgroup *p)
> +{
> +	while (1) {
> +		int64_t old_mark, new_mark, cur_mark;
> +
> +		old_mark = atomic64_read(&p->highwater_mark);
> +		new_mark = atomic64_read(&p->counter);
> +		if (old_mark >= new_mark)
> +			return;
> +		cur_mark = atomic64_cmpxchg(&p->highwater_mark, old_mark,
> +					    new_mark);
> +
> +		/* It's OK if the counter was decreased meanwhile */
> +		if (cur_mark == old_mark &&
> +		    atomic64_read(&p->counter) <= new_mark)
> +			return;
> +	}
> +}

I think it'd be better to make this part of pids_charge() - maybe use
atomic64_add_return() to get the current value and track the maximum?

> @@ -300,6 +341,11 @@ static struct cftype pids_files[] = {
>  		.read_s64 = pids_current_read,
>  		.flags = CFTYPE_NOT_ON_ROOT,
>  	},
> +	{
> +		.name = "highwater_mark",
> +		.read_s64 = pids_highwater_mark_read,
> +		.flags = CFTYPE_NOT_ON_ROOT,
> +	},

This should be an entry in the pids.stats file.  Please also update
the documentation accordingly.

Thanks.

-- 
tejun