Re: [2.6.17.4] slabinfo.buffer_head increases

[Nick Piggin <nickpiggin@yahoo.com.au>]

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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