linux-kernel - Re: Why kmem_cache_free occupy CPU for more than 10 seconds?

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Date:	Wed, 11 Apr 2007 12:16:55 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Zhao Forrest <forrest.zhao@...il.com>
Cc:	Paul Jackson <pj@....com>, penberg@...helsinki.fi,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: Why kmem_cache_free occupy CPU for more than 10 seconds?

On Wed, 2007-04-11 at 18:10 +0800, Zhao Forrest wrote:
> On 4/11/07, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > On Wed, 2007-04-11 at 02:53 -0700, Paul Jackson wrote:
> > > I'm confused - which end of ths stack is up?
> > >
> > > cpuset_exit doesn't call do_exit, rather it's the other
> > > way around.  But put_files_struct doesn't call do_exit,
> > > rather do_exit calls __exit_files calls put_files_struct.
> >
> > I'm guessing its x86_64 which generates crap traces.
> >
> Yes, it's x86_64. Is there a reliable way to generate stack traces under x86_64?
> Can enabling "[ ] Compile the kernel with frame pointers" help?

Sometimes, the best is to redo the undo of the dwarf based stack
unwinder.

But as you said, that _huge_ number of buffers might be the issue, I'm
looking through the codepaths from __blkdev_put on downwards, I suspect
we hold a single lock somewhere,...

So hold on with patching the unwinder back in (unless of course you
fancy doing so :-)



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