Subject: Re: [LTP] [PATCH 1/8] Scaling msgmni to the amount of lowmem
From: Subrata Modak <subrata@linux.vnet.ibm.com>
Reply-To: subrata@linux.vnet.ibm.com
To: Nadia Derbey <Nadia.Derbey@bull.net>
Cc: Andrew Morton <akpm@linux-foundation.org>, ltp-list@lists.sourceforge.net,
       containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, cmm@us.ibm.com, matthltc@us.ibm.com,
       y-goto@jp.fujitsu.com
In-Reply-To: <47BB0EDC.5000002@bull.net>
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	 <1203411055.4612.5.camel@subratamodak.linux.ibm.com>
	 <47BB0EDC.5000002@bull.net>
Content-Type: text/plain
Organization: IBM
Date: Wed, 20 Feb 2008 15:14:55 +0530
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> Subrata Modak wrote:
> >>Nadia Derbey wrote:
> >>
> >>>Andrew Morton wrote:
> >>>
> >>>
> >>>>On Mon, 11 Feb 2008 15:16:47 +0100 Nadia.Derbey@bull.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.
> >>>
> >>
> >>Well, actually, the test does not block, it only takes much much more 
> >>time to be executed:
> >>
> >>doing this:
> >>date; ./msgctl08 100000 XXX; date
> >>
> >>
> >>gives us the following results:
> >>XXX           16   32   64   128   256   512   1024   1746
> >>time(secs)     2    4    8    16    32    64    132    241
> >>
> >>XXX is the # of msg queues to be created = # of processes to be forked 
> >>as readers = # of processes to be created as writers
> >>time is approximative since it is obtained by a "date" before and after.
> >>
> >>XXX used to be 16 before the patchset  ---> 1st column
> >>     --> 16 processes forked as reader
> >>     --> + 16 processes forked as writers
> >>     --> + 16 msg queues
> >>XXX = 1746 (on my victim) after the patchset ---> last column
> >>     --> 1746 reader processes forked
> >>     --> + 1746 writers forked
> >>     --> + 1746 msg queues created
> >>
> >>The same tests on the ref kernel give approximatly the same results.
> >>
> >>So if we don't want this longer time to appear as a regression, the LTP 
> >>should be changed:
> >>1) either by setting the result of get_max_msgqueues() as the MSGMNI 
> >>constant (16) (that would be the best solution in my mind)
> >>2) or by warning the tester that it may take a long time to finish.
> >>
> >>There would be 3 tests impacted:
> >>
> >>kernel/syscalls/ipc/msgctl/msgctl08.c
> >>kernel/syscalls/ipc/msgctl/msgctl09.c
> >>kernel/syscalls/ipc/msgget/msgget03.c
> > 
> > 
> > We will change the test case if need that be. Nadia, kindly send us the
> > patch set which will do the necessary changes.
> > 
> > Regards--
> > Subrata
> > 
> 
> Subrata,
> 
> You'll find the patch in attachment.
> FYI I didn't change msgget03.c since we need to get the actual max value 
> in order to generate an error.

Thanks. The same has been Merged.

Regards--
Subrata

> 
> Regards,
> Nadia
> 

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