Re: 2.6.36 io bring the system to its knees

[Ingo Molnar]

* Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:

> 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@xxxxxxxxx> 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.

Seeking in a file and fsync-ing it does not seem like an inherently bad or even 
stupid thing to do - why do you claim that it is stupid?

If mixed seek()+fsync() is the reason for these latencies (which is just an 
assumption right now) then it needs to be fixed in the kernel, not in apps.

Thanks,

	Ingo
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