Structure and Interpretation of Computer Programmers

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Sunday, February 25, 2007

Apres ca, le FOSDEM

It appears that I’m sat in Terminal B of L’Aeroporte Nationale de Bruxelles, waiting for my flight to board. While there are wirelesses around, the ones to which I can connect seem not to be offering much in the way of DHCP so this update will come in later than it was written (which was at 13:35), as I will probably post it while I’m on the bus between Heathrow and Oxford. [Update: actually not until I got home]

Irrelevancies such as that aside, I had a great FOSDEM! In fact, a great half-FOSDEM, as I did my tourism today. I met a load of people (of which more below), went to some inspiring talks and discussed many exciting and interesting projects (in multiple languages – I spoke to one person in English, Dutch and French sometimes in the same sentence). It was a good exercise to see who wasn’t present as much as who was – for instance RedHat didn’t have an official presence although the Fedora Project had a booth (next to the CentOS one ;-), similarly Novell (one of the big sponsors) was absent but the OpenSUSE project had Yet Another Small Table. Sun were conspicuously present in that the OpenSolaris and OpenJDK table was being manned seemingly by Sun’s salespeople rather than user group members…although maybe that’s just my interpretation.

The overriding feeling I got was that the conference was running on l’espirit d’anarchie and that the resulting adrenaline and enthusiasm drove the conference on. The keynote speeches were really the only regimented aspect of FOSDEM – a necessity given the size of the auditorium and that was packed to the rafters with FLOSSers. I didn’t go to the final keynote on open-sourcing Java as I was manning the GNUstep booth, but learned a lot on software patents and Free Software and Jim Gettys’ description of the technical challenges in creating OLPC was very insightful.

So, GNUstep. GNUstep, GNUstep, Etoile [I’ll add the accents in in a later update…this keyboard doesn’t have dead keys :-(]. For a start it was great to meet all the other GNUsteppers, and have some good discussions and debates (as well as some good moule frites and Kwak beer). For anyone who doubts that GNUstep is still alive, the dev room at FOSDEM is one place to allay such suspicions with many developers, designers, users and supporters presenting their ideas to each other, asking each other questions and generally contributing to the GNUstep camaraderie. Even an improptu troll by Miguel de Icaza at the GNUstep booth wasn’t enough to make us all throw Project Center away and buy a book on C# ;-). Presentations on GNUstep-make v2 (which I’ve described here before…), the Cairo graphics back-end (which I don’t think Fred Kiefer was expecting to present, but made a very fine job of it anyway) and third-party use of GNUstep were all very useful and well-received…I expect today’s presentations were too but I didn’t get to go to them :-(. [Instead, I was significantly underwhelmed by the sight of the Mannekin Pis.]

posted by Graham Lee at 18:27  

Tuesday, February 20, 2007

Fairly cool update to GNUstep

GNUstep-make now supports arbitrary(-ish) filesystem layouts. While the default is still the /usr/GNUstep layout with the various domains, one of the bundled alternatives is to put everything in FHS-compliant locations. Once that hits a release (which I believe will be called gnustep-make 2.0), that should make newbie users and distributors much more comfortable with GNUstep. I also provided a NeXT-ish layout which doesn’t clone the NeXT directory hierarchy, but rather mimics it sensitively.

My work laptop just earned itself a reinstall (I’d been uncomfortable with CentOS for a while, but the facts that hotplug isn’t configured properly and every time I ‘yum update’ I have to fix a handful of drivers drove me over the edge), so when I re-create my GNUstep installation I’ll do it with the new-style make. I’m currently wavering on the side of installing Midnight BSD, but I might wimp out and dual-boot Ubuntu ;-)

posted by Graham Lee at 18:33  

Friday, January 12, 2007

Eating one’s own dog food

I feel foolish for having made this error (especially after having so patiently explained how this stuff works on Mach), but today I did it. I reported the amount of free memory on a Linux system as being the amount reported by free as free.

My own opinion on this is that I suffer from a view of hardware management which was tainted by using micros like the Dragon 32 (Radio Shack/Tandy TRS-80 to my American readers) and the Amiga, where there were basically two types of memory usage: yes and no. A particular block was either in use by the system, or it wasn’t. On the Dragon 32 it was even easier than that of course; all bytes were available for reading and writing, but what happened was context-dependent. Also because this was the MC6809E, whether such a peek/poke made sense depended on whether you were trying to hit an I/O address, and what was plugged in. The Amiga had a particularly lame memory allocator which quickly sucked performance like a vacuum of performance suckage +2; but a byte of RAM was either in use or it was available.

But I digress. The point is, that such a simple view of memory availability is no longer sensible but it’s hard for me to think around it without a lot of work, just as it was hard for me to become a programmer after I’d been taught BASIC and Pascal. If I were involved in UNIX internals more (and indeed that would be fun, although I think maybe Linux wouldn’t be my first choice to open up) I’d probably be able to think about these things properly, just as I had to throw myself into C programming in a big way before I lost my BASIC-isms.

For the record (and so that it looks like this post is going somewhere), both operating systems have an intermediate state for RAM to be in between "used" and "not used" (where I’m ignoring kernel wired memory, and Linux kernel buffers). On Mach, there’s the "inactive" state which I’ve already described at el linko above. On Linux, it’s used as an I/O cache for (mainly disk, mainly read-ahead) operations. This means that Linux will automatically take almost all (if not all) of the memory during the boot process. The way that inactive memory gets populated on Mach means that on that system (e.g. Darwin) actually the amount of free memory starts large and inactive starts small, but over time as the active and inactive counts go up, the free count goes down, and it’s rare for memory to be re-freed. On both systems, free memory is really "memory it wasn’t worth you buying" as it’s not being put to any use at all.

posted by Graham Lee at 18:05  

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