linux-kernel - Re: 2.6.39-rc4+: Kernel leaking memory during FS scanning, regression?

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Date:	Mon, 25 Apr 2011 20:36:06 +0200
From:	Bruno Prémont <bonbons@...ux-vserver.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mike Frysinger <vapier.adi@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	Pekka Enberg <penberg@...nel.org>
Subject: Re: 2.6.39-rc4+: Kernel leaking memory during FS scanning,
 regression?

On Mon, 25 April 2011 Linus Torvalds wrote:
> On Mon, Apr 25, 2011 at 10:00 AM, Bruno Prémont wrote:
> >
> > I hope tiny-rcu is not that broken... as it would mean driving any
> > PREEMPT_NONE or PREEMPT_VOLUNTARY system out of memory when compiling
> > packages (and probably also just unpacking larger tarballs or running
> > things like du).
> 
> I'm sure that TINYRCU can be fixed if it really is the problem.
> 
> So I just want to make sure that we know what the root cause of your
> problem is. It's quite possible that it _is_ a real leak of filp or
> something, but before possibly wasting time trying to figure that out,
> let's see if your config is to blame.

With changed config (PREEMPT=y, TREE_PREEMPT_RCU=y) I haven't reproduced
yet.

When I was reproducing with TINYRCU things went normally for some time
until suddenly slabs stopped being freed.

> > And with system doing nothing (except monitoring itself) memory usage
> > goes increasing all the time until it starves (well it seems to keep
> > ~20M free, pushing processes it can to swap). Config is just being
> > make oldconfig from working 2.6.38 kernel (answering default for new
> > options)
> 
> How sure are you that the system really is idle? Quite frankly, the
> constant growing doesn't really look idle to me.

Except the SIGSTOPed build there is not much left, collectd running in
background (it polls /proc for process counts, fork rate, memory usage,
... opening, reading, closing the files -- scanning every 10 seconds),
slabtop on one terminal.

CPU activity was near-zero with 10%-20% spikes of system use every 10
minutes and io-wait when all cache had been pushed out.

> > Attached graph matching numbers of previous mail. (dropping caches was at
> > 17:55, system idle since then)
> 
> Nothing at all going on in 'ps' during that time? And what does
> slabinfo say at that point now that kmemleak isn't dominating
> everything else?

ps definitely does not show anything special, 30 or so userspace processes.
Didn't check ls /proc/*/fd though. Will do at next occurrence.


Going to test further with various PREEMPT and RCU selections. Will report
back as I progress (but won't have much time tomorrow).

Bruno
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