linux-kernel - Re: [PATCH 0/3] Make tasks always have non-zero pids

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Message-ID: <20071005055317.GB28111@us.ibm.com>
Date:	Thu, 4 Oct 2007 22:53:17 -0700
From:	sukadev@...ibm.com
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...nvz.org, Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH 0/3] Make tasks always have non-zero pids

Pavel Emelianov [xemul@...nvz.org] wrote:
| Some time ago Sukadev noticed that the vmlinux size has

Cedric pointed it out to me first :-)

| grown 5Kb due to merged pid namespaces. One of the big
| problems with it was fat inline functions. The other thing
| was noticed by Matt - the checks for task's pid to be not
| NULL take place and make the kernel grow due to inlining,
| but these checks are not always needed.
| 
| In this series I introduce a static pid (dummy), according
| to Matt's proposal, which is assigned to tasks during the 
| detach_pid and transfer_pid instead of NULL. This pid lives 
| in the init pid namespace and has the id = 0, so all the 
| task_xid_xnr() calls will still return 0 on a dead task.
| 
| Places that get the struct pid from task either get it from
| the current (in this case they will never get this dummy),
| or use it to compare with some other value (so they will 
| work the same for both NULL and dummy pids).
| 
| This saves up to 340 bytes for i386 kernel with minimal 
| config  and probably more with more users of pids.
| 
| Tested on i386 and x86_64 boxes. Tasks still live and die,
| namespaces and proc still work.
| 
| Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>

Acked-by: Sukadev Bhattiprolu <sukadev@...ibm.com>
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