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

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Message-ID: <47BB0EDC.5000002@bull.net>
Date:	Tue, 19 Feb 2008 18:16:12 +0100
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	subrata@...ux.vnet.ibm.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	ltp-list@...ts.sourceforge.net,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, cmm@...ibm.com,
	matthltc@...ibm.com, y-goto@...fujitsu.com
Subject: Re: [LTP] [PATCH 1/8] Scaling msgmni to the amount of lowmem

Subrata Modak wrote:
>>Nadia Derbey wrote:
>>
>>>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.
>>>
>>
>>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.

Regards,
Nadia


View attachment "ipc_ltp_full_20080131.patch" of type "text/x-patch" (6297 bytes)