Bellicose Bumpkin

I’ve been playing around with several Linux distributions on my old Dell D600 laptop. Initially I threw Ubuntu 9.1(Karmic Koala) on it but had problems with the desktop freezing every time I started up an application. I got around that by putting on some alternate desktop environments that I’d been wanting to play around with including XFCE, Fluxbox, and IceWM. Shortly after getting it installed, the disk died so I figured I’d try out some other Ubuntu related distributions. I tried Kubuntu – a KDE based(versus Gnome) based distro. I tried out my old favorite Mepis Linux and last but not least Linux Mint 8 Helena. There are great reviews of Linux Mint out there. This is not one of them. This post is to help others with freezing issues related to Dell D600 laptops and Ubuntu-based distributions.
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Linux Mint is also Ubuntu based but includes proprietary codecs and a highly customized theme that looks very different from Ubuntu. With Linux being an open source operating system, most distrubutions do not include any proprietary software. Most users will expend some effort to get support for playing mp3, windows media files, quicktime, and encrypted dvds. Mint includes all that.
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My install had the same problems as most of the Ubuntu 9.1 based distros I’ve been trying lately – it froze. This freezing issue seems to be related to Compiz and probably the X driver for the laptop’s video card – an ATI Mobility Radeon 9000. Selecting the OEM install got me through the installation problem – but still had the freezing issue when starting all or most applications. That was solved by right clicking on the desktop and setting the desktop effects to “none”. You lose some of the spiffy effects on the desktop but actually get a more responsive desktop. The D600 is getting a little long in the tooth and doesn’t have the horsepower for overly flashy desktop effects.
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Linux Mint has an interesting looking desktop – quite different from the Ubuntu and Redhat based distributions I usually run. My first impression is very positive – it is an attractive environment and feels very responsive. It will be getting a good workout here at home – particularly with the kids. They’ll be using it when the main computer (Windows XP) is occupied. My 8 year old was using it last night to watch a Star Wars/Clone Wars episode he missed and to browse for Star Wars Legos on Amazon. So much for Linux being too difficult to use.

This post is pure geek. You’ve been warned.

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I came across an interesting gotcha in Linux 2.6 kernels that I’ve never seen before despite the fact that I’ve been running 2.6 kernels for a number of years.

It’s called the oom-killer. Bwahahaha…

I came across this when my virtual machine died while running a build. The /var/log/messages log showed:

May 30 00:02:33 localhost kernel: oom-killer: gfp_mask=0xd0May 30 00:02:36 localhost kernel: cpu 0 hot: low 32, high 96, batch 16May 30 00:02:36 localhost kernel: cpu 0 cold: low 0, high 32, batch 16May 30 00:02:36 localhost kernel: cpu 1 hot: low 32, high 96, batch 16May 30 00:02:36 localhost kernel: cpu 1 cold: low 0, high 32, batch 16May 30 00:02:36 localhost kernel: May 30 00:02:36 localhost kernel: Free pages: 35932kB (19712kB HighMem)May 30 00:02:39 localhost kernel: HighMem free:19712kB min:512kB low:1024kB high:1536kB active:1002148kB inactive:1422792kB present:2488324kB pages_scanned:0 all_unreclaimable? noMay 30 00:02:39 localhost kernel: protections[]: 0 0 0May 30 00:02:40 localhost kernel: DMA: 1*4kB 3*8kB 4*16kB 2*32kB 3*64kB 3*128kB 2*256kB 0*512kB 1*1024kB 1*2048kB 2*4096kB = 12508kBMay 30 00:02:43 localhost kernel: Free swap: 4176688kBMay 30 00:02:44 localhost kernel: 851457 pages of RAMMay 30 00:02:44 localhost kernel: 622081 pages of HIGHMEMMay 30 00:02:44 localhost kernel: 8252 reserved pagesMay 30 00:02:44 localhost kernel: 748042 pages sharedMay 30 00:02:44 localhost kernel: 2173 pages swap cachedMay 30 00:02:44 localhost kernel: Out of Memory: Killed process 4300 (vmware-vmx

The oom-killer is the Out Of Memory killer and is described here:

By default, the Linux kernel is configured to never say no when application processes ask for more memory. The assumption is that the applications will not actually use all the memory they ask for–this is called overcommitting memory. Hotels and airlines do the same thing when accepting bookings: the assumption is that not everybody who makes a booking will actually turn up to take their room/flight.

However, every now and then, the assumption is wrong–you have an overbooking, and somebody has to get bumped. When Linux runs out of memory, it starts killing processes in order to free some up. Of course, the processes are chosen according to a heuristic (which is a technical term meaning “you can’t please everyone”), and so invariably the kernel is going to kill something you consider important, thereby leading to much wailing and gnashing of teeth.

There are a number of ways of stopping this:

• Check for low memory exhaustion

  # egrep 'High|Low' /proc/meminfo

  # free -lm

  When low memory is exhausted, it doesn’t matter how much high memory is
  available, the oom-killer will begin whacking processes to keep the
  server alive.

• upgrade to 64-bit linux(not an option for most)
• If limited to 32-bit Linux, the best solution is to run the hugemem kernel. This kernel splits low/high memory differently, and in most cases should provide enough low memory to map high memory. In most cases this is an easy fix – simply install the hugemem kernel RPM & reboot.
• If running the 32-bit hugemem kernel isn’t an option either, you can try setting /proc/sys/vm/lower_zone_protection to a value of 250 or more. This will cause the kernel to try to be more aggressive in defending the low zone from allocating memory that could potentially be allocated in the high memory zone. As far as I know, this option isn’t available until the 2.6.x kernel. Some experimentation to find the best setting for your environment will probably be necessary. You can check & set this value on the fly via:

      # cat /proc/sys/vm/lower_zone_protection    # echo "250" > /proc/sys/vm/lower_zone_protection

  To set this option on boot, add the following to /etc/sysctl.conf:

      vm.lower_zone_protection = 250

• As a last-ditch effort, you can disable the oom-killer. This option can cause the server to hang, so use it with extreme caution (and at your own risk)!

      Check status of oom-killer:    # cat /proc/sys/vm/oom-kill
  
      Turn oom-killer off/on:    # echo "0" > /proc/sys/vm/oom-kill    # echo "1" > /proc/sys/vm/oom-kill
  
      To make this change take effect at boot time, add the following to /etc/sysctl.conf:    vm.oom-kill = 0