linux-kernel - Re: [PATCH 1/8] Scaling msgmni to the amount of lowmem

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Date:	Mon, 18 Feb 2008 10:19:08 +0100
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, y-goto@...fujitsu.com,
	linux-mm@...ck.org, containers@...ts.linux-foundation.org,
	matthltc@...ibm.com, cmm@...ibm.com
Subject: Re: [PATCH 1/8] Scaling msgmni to the amount of lowmem

Andrew Morton wrote:
> On Mon, 11 Feb 2008 15:16:47 +0100 Nadia.Derbey@...l.net wrote:
> 
> 
>>[PATCH 01/08]
>>
>>This patch computes msg_ctlmni to make it scale with the amount of lowmem.
>>msg_ctlmni is now set to make the message queues occupy 1/32 of the available
>>lowmem.
>>
>>Some cleaning has also been done for the MSGPOOL constant: the msgctl man page
>>says it's not used, but it also defines it as a size in bytes (the code
>>expresses it in Kbytes).
>>
> 
> 
> Something's wrong here.  Running LTP's msgctl08 (specifically:
> ltp-full-20070228) cripples the machine.  It's a 4-way 4GB x86_64.
> 
> http://userweb.kernel.org/~akpm/config-x.txt
> http://userweb.kernel.org/~akpm/dmesg-x.txt
> 
> Normally msgctl08 will complete in a second or two.  With this patch I
> don't know how long it will take to complete, and the machine is horridly
> bogged down.  It does recover if you manage to kill msgctl08.  Feels like
> a terrible memory shortage, but there's plenty of memory free and it isn't
> swapping.
> 
> 
> 

Before the patchset, msgctl08 used to be run with the old msgmni value: 
16. Now it is run with a much higher msgmni value (1746 in my case), 
since it scales to the memory size.
When I call "msgctl08 100000 16" it completes fast.

Doing the follwing on the ref kernel:
echo 1746 > /proc/sys/kernel/msgmni
msgctl08 100000 1746

makes th test block too :-(

Will check to see where the problem comes from.

Rgards,
Nadia
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