Re: Linux 2.6.31 - very swap-happy with plenty of free RAM

[Tomasz Chmielewski]

Dave Chinner wrote:

> > > > I have a pretty powerful desktop machine with 8 GB RAM, fast disks with
> > > > RAID-1 etc.
> > > > Every 10 minutes or so, machine is really unresponsive, load jumps to 10 or
> > > > 20. Mouse pointer jumps, it's impossible to change between windows etc.
> > > This is the type of hefty workstation many of the core developers
> > > have, running similar workloads, so I'm somewhat surprised that the
> > > default VM settings have this kind of issue.
> > >
> > > > Do a "swapoff -a", and everything is snappy and responsive as it should,
> > > > there are no more lags.
> > > Yes, that's my exact finding.
> > >
> > > Is this weird IO storm happening for anyone else with plenty of memory
> > > (for their taskload?)
> > For me it happend on my laptop. 3gb RAM, and a 1gb VMWare Windows-XP 
> > instance running, plus the usual like firefox, thunderbird, kde4.
> >
> > Without running vmware it did not happen. And since I have now disabled 
> > barriers on the xfs /home partition (on luks crypto lvm) it also does 
> > not happen anymore.
>
> Yeah, it looks like dm-crypt recently started supporting barriers in
> commit 647c7db14ef9cacc4ccb3683e206b61f0de6dc2b. Hence XFS will have
> detected barriers work at mount time mount and so is now issuing
> them.
>
> Similarly, raid1 (mirror) has recently gained barrier support so
> the same issue can be seen there.

What is also interesting, that a normal software RAID-1 sync (i.e. from 
a degraded state) does not seem to make any visible effect on system 
responsiveness.

Uncompress a big tar file, or VM writes out lots of data - system 
becomes really unresponsive.


--
Tomasz Chmielewski
http://wpkg.org
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