linux-kernel - Re: [PATCH 1/1] Only output msgmni value at boot time

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Date:	Thu, 29 May 2008 11:43:33 +0200
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Only output msgmni value at boot time

Luck, Tony wrote:
>>In http://lkml.org/lkml/2008/4/29/575 Tony Luck complained that this message
>>references an ipc namespace address that is useless.
>>
>>I first thought of using an audit_log instead of a printk, as suggested by
>>Serge Hallyn. But unfortunately, we do not have any other information than
>>the namespace address to provide here too.
>>So I chose to move the message and output it only at boot time, removing the
>>reference to the namespace.
> 
> 
> Diffing my before/after dmesg(8) output:
> < msgmni has been set to 7964 for ipc namespace a000000100a1ad58
> ---
> 
>>msgmni has been set to 7964
> 
> 
> Much prettier.  Thank you.
> 
> I'll leave it to SGI to ponder whether it is correct to compute
> msgmni based on a linear function of lowmem (their big systems can
> have terabytes of memory, all of which is counted as lowmem).

Sure that if the formula can be enhanced, that would be great.
But don't forget 2 things:
. msgmni cannot become higher than IPCMNI: i.e. starting from 16Gb of 
lowmem, and based on a value of 16K for msgmnb, msgmni won't increase. 
(if I'm not wrong in my computation).
. there is no memory pre-allocation done based upon msgmni value: by 
increasing its value we are just making the DoS (for too many msg 
queues) come later.
. there is still the possibility of lowering the value "by hand" (via 
procfs) if ever it is found to be too high.

Regards,
Nadia

> 
> 
>>This patch applies to 2.6.26-rc2-mm1.
> 
> 
> Acked-by: Tony Luck <tony.luck@...el.com>
> 
> Signed-off-by: Nadia Derbey <Nadia.Derbey@...l.net>
> 
> ---
>  ipc/msg.c |   13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> Index: linux-2.6.26-rc2-mm1/ipc/msg.c
> ===================================================================
> --- linux-2.6.26-rc2-mm1.orig/ipc/msg.c	2008-05-26 12:25:37.000000000 +0200
> +++ linux-2.6.26-rc2-mm1/ipc/msg.c	2008-05-27 10:59:34.000000000 +0200
> @@ -98,20 +98,15 @@ void recompute_msgmni(struct ipc_namespa
>  
>  	if (allowed < MSGMNI) {
>  		ns->msg_ctlmni = MSGMNI;
> -		goto out_callback;
> +		return;
>  	}
>  
>  	if (allowed > IPCMNI / nb_ns) {
>  		ns->msg_ctlmni = IPCMNI / nb_ns;
> -		goto out_callback;
> +		return;
>  	}
>  
>  	ns->msg_ctlmni = allowed;
> -
> -out_callback:
> -
> -	printk(KERN_INFO "msgmni has been set to %d for ipc namespace %p\n",
> -		ns->msg_ctlmni, ns);
>  }
>  
>  void msg_init_ns(struct ipc_namespace *ns)
> @@ -136,6 +131,10 @@ void msg_exit_ns(struct ipc_namespace *n
>  void __init msg_init(void)
>  {
>  	msg_init_ns(&init_ipc_ns);
> +
> +	printk(KERN_INFO "msgmni has been set to %d\n",
> +		init_ipc_ns.msg_ctlmni);
> +
>  	ipc_init_proc_interface("sysvipc/msg",
>  				"       key      msqid perms      cbytes       qnum lspid lrpid   uid   gid  cuid  cgid      stime      rtime      ctime\n",
>  				IPC_MSG_IDS, sysvipc_msg_proc_show);
> 




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