Huge instability and insanely large memory footprint in 9.04

[Evan]

On Fri, Sep 25, 2009 at 8:19 AM, Evan <eapache at gmail.com> wrote:

> On Fri, Sep 25, 2009 at 7:40 AM, Marius Gedminas <marius at pov.lt> wrote:
>
>> On Fri, Sep 18, 2009 at 04:46:21AM -0700, J. Lennard wrote:
>> > First I'm sorry to write what may appear as a rant, but I hope it is
>> > not considered so. I'm writing to express huge instability problems in
>> > Ubuntu 9.04. I migrated from ubuntu 8.04 (386) to ubuntu 9.04 (amd64)
>> > using a simple clean install.
>> ...
>> > I don't really know where to start. During past month, my machine
>> > constantly went to trashing mode where the hard-disk light is
>> > constantly on and I can't access anything or even swtich to linux
>> > console for several *minutes*. This has occured more than four times
>> > although all I usually run is a pdf viewer, an mp3 player, emacs, and
>> > firefox with simple html pages (not even gmail, flash, etc).
>>
>> Do you have any swap space?
>>
>> I've got an Asus EeePC 900 with 1 GB of RAM.  Twice now I've experienced
>> the same thing: constant disk I/O, huge latencies for any desktop task
>> (switching windows, launching terminals).  I suspect a bug in the Linux
>> VM subsystem, since *I was not running out of memory*.  Usually about
>> 40-50% of my RAM is in disk cache---I keep track of memory usage via a
>> GNOME panel applet.  On those occasions cache size was shrinking,
>> completely free memory was increasing, all application pages were being
>> constantly swapped out and back in causing constant disk I/O (which is
>> painful on an SSD).  The fix was to create a temporary swap file in
>> /tmp:
>>
>>  sudo -s
>>  dd if=/dev/zero of=/tmp/swapfile bs=1M count=1024
>>  mkswap /tmp/swapfile
>>  swapon /tmp/swapfile
>>
>> Instantly the system became responsible again, after using ~400
>> *kilobytes* of swap.
>>
>> I can only assume that having 0 swap space confused the VM somehow and
>> kicked it into a full-on panic "let's free all the ram we can" mode.
>>
>> This swap file disappears after a reboot, and so far the problem hasn't
>> recurred, so I didn't bother setting up a permanent swap partition (I'm
>> afraid to destroy my SSD too quickly with constant writes---this already
>> happened once thanks to ext3's journal).
>>
>
> I have had this occur several times to me on a quad-core with 3GB ram (and
> 6GB swap), but only ever when resuming. If I suspend with all free memory
> used by cache (according to the Gnome panel applet), then occasionally on
> resume it spends ~5minutes unresponsive with massive disk IO before coming
> up. When it does come back everything is fine, except that all of that space
> which was cache is now completely empty. I set my vm.swappiness value to 0
> (because I so rarely need it), so while I'm definitely not running out of
> swap space, I can see how swappiness=0 might cause the same sort of effect.
> I haven't found anything odd in the logs so I never filed a bug, but if it's
> happening to other people in other situations this bears investigating. I
> will open a bug on this as soon as I have time.
>

This bug finally reoccurred, and I caught something in the log files this
time. The bug is at

https://bugs.launchpad.net/ubuntu/+source/pm-utils/+bug/438889

Mine appears to be in pm-utils, so I doubt it's the same as yours Marius,
but it may be a more fundamental problem with the kernel's memory
management. It's worth taking a look at in any case.

Evan
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