linux-kernel - Re: [2.6.17.4] slabinfo.buffer

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Date:	Wed, 13 Sep 2006 12:32:41 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Guennadi Liakhovetski <gl@...-ac.de>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [2.6.17.4] slabinfo.buffer_head increases

Guennadi Liakhovetski wrote:
> On Tue, 12 Sep 2006, Nick Piggin wrote:
> 
>> Guennadi Liakhovetski wrote:
>>
>>>> On Mon, 10 Jul 2006, Guennadi Liakhovetski wrote:
>>>>
>>>>> I am obsering a steadily increasing buffer_head value in slabinfo 
>>>>> under
>>>>> 2.6.17.4. I searched the net / archives and didn't find anything
>>>>> directly relevant. Does anyone have an idea or how shall we debug it?
>>>>
>>>>
>>>
>>> The problem is still there under 2.6.18-rc2. I narrowed it down to 
>>> ext3 journal. To reproduce one just has to mount an ext3 partition 
>>> and perform (write) accesses to it. A loop { touch /mnt/foo; sleep 1; 
>>> } suffices - just let it run for a couple of minutes and monitor 
>>> buffer_head in /proc/slabinfo. If you mount it as ext2 the problem is 
>>> gone.
>>
>>
>>
>> What data mode is ext3 mounted with?
> 
> 
> Default, i.e., ordered, I guess.
> 
>> Is the memory reclaimable? If yes, is it a problem?
> 
> 
> Yes, that's why I later wrote that the problem is not real. It was hard 
> to see as we had a lot of free RAM on the system, the system was idle 
> apart from one script that only did "touch x" periodically with the same 
> "x" and the buffer_head slab was growing very steadily. Unlike with ext2 
> / reiserfs. That's why I decided it was not ok. But the memory is 
> reclaimable, so, seems like not a problem. Just a bit odd that such a 
> "harmless" operation causes a steady growth of buffer_heads...

OK. It is just a quirk in the way that ext3 ordered interacts with page freeing
and reclaim, I think. If it is causing you no performance problems then that's
good. Though it is counter intuitive.

Thanks for the report anyway.

-- 
SUSE Labs, Novell Inc.
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