linux-kernel - Re: [PATCH 1/3] Adds a read-only "procs" file similar to "tasks" that shows only unique tgids

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Message-Id: <1247596470.13426.16088.camel@nimitz>
Date:	Tue, 14 Jul 2009 11:34:30 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Ben Blum <bblum@...gle.com>
Cc:	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, akpm@...ux-foundation.org,
	serue@...ibm.com, lizf@...fujitsu.com, menage@...gle.com
Subject: Re: [PATCH 1/3] Adds a read-only "procs" file similar to "tasks"
 that shows only unique tgids

On Fri, 2009-07-10 at 16:01 -0700, Ben Blum wrote:
> +struct cgroup_pidlist {
> +       /* protects the other fields */
> +       struct rw_semaphore mutex;
> +       /* array of xids */
> +       pid_t *list;
> +       /* how many elements the above list has */
> +       int length;
> +       /* how many files are using the current array */
> +       int use_count;
> +};

I think a slightly nicer way of doing this would be to use a structure
like this:

#define NR_PIDS (PAGE_SIZE-sizeof(struct list_head))
struct pid_list {
	struct list_head list;
	pid_t pids[NR_PIDS];
};

That way, you can always kmalloc(sizeof(pid_list)), it fits nicely in
PAGE_SIZE, and you can chain them together.

Or, you could always just use one of the other flexible structures in
the kernel like a radix_tree.

-- Dave

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