linux-kernel - Re: [PATCH 5/20] Introduce struct upid

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Message-ID: <20070908021656.GA21860@us.ibm.com>
Date:	Fri, 7 Sep 2007 19:16:56 -0700
From:	sukadev@...ibm.com
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	xemul@...nvz.org, devel@...nvz.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, oleg@...sign.ru
Subject: Re: [PATCH 5/20] Introduce struct upid

Andrew Morton [akpm@...ux-foundation.org] wrote:
| On Fri, 10 Aug 2007 15:47:59 +0400
| xemul@...nvz.org wrote:
| 
| >  struct pid
| >  {
| >  	atomic_t count;
| > @@ -50,6 +50,8 @@ struct pid
| >  	/* lists of tasks that use this pid */
| >  	struct hlist_head tasks[PIDTYPE_MAX];
| >  	struct rcu_head rcu;
| > +	int level;
| > +	struct upid numbers[1];
| 
| You can make this have size [0] now.  It's a gcc extension and
| is used elsewhere in the kernel.

Sorry, we did not respond to this yet :-)

Well, every process has at least one 'struct upid'. The only "cost"
I see with size [1] is having to subtract 1 in create_pid_cachep().

Besides, we create/initialize the 'struct pid' for the idle process
by hand (see INIT_STRUCT_PID in init_task.h).

If we set this size to [0] now, we would need to dynamically allocate
a 'struct upid' during early boot and attach this upid to init_struct_pid.

Or is there a easy way to attach a 'upid' to init_struct_pid, statically ?

Suka

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