Re: [2.6.17.4] slabinfo.buffer_head increases

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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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