linux-kernel - Re: 2.6.36 io bring the system to its knees

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Date:	Thu, 28 Oct 2010 09:46:41 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Aidar Kultayev <the.aidar@...il.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	npiggin@...nel.dk, Dave Chinner <david@...morbit.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: 2.6.36 io bring the system to its knees

On Thu, Oct 28, 2010 at 02:48:20PM +0300, Pekka Enberg wrote:
> On Thu, Oct 28, 2010 at 2:33 PM, Aidar Kultayev <the.aidar@...il.com> wrote:
> > if it wasn't picasa, it would have been something else. I mean if I
> > kill picasa ( later on it was done indexing new pics anyway ), it
> > would have been for virtualbox to thrash the io. So, nope, getting rid
> > of picasa doesn't help either. In general the systems responsiveness
> > or sluggishness is dominated by those io operations going on - the DD
> > & CP & probably VBOX issuing whole bunch of its load for IO.
> 
> Do you still see high latencies in vfs_lseek() and vfs_fsync()? I'm
> not a VFS expert but looking at your latencytop output, it seems that
> fsync grabs ->i_mutex which blocks vfs_llseek(), for example. I'm not
> sure why that causes high latencies though it's a mutex we're holding.

It does.  But what workload does a lot of llseeks while fsyncing the
same file?  I'd bet some application is doing really stupid things here.

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