Unix virtual memory when you have no swap space, Dsynth details on Dragonfly, Instant Workstation on FreeBSD, new servers new tech, Experimenting with streaming setups on NetBSD, NetBSD’s progress towards Steam support thanks to GSoC, and more.
Headlines
What has to happen with Unix virtual memory when you have no swap space (https://utcc.utoronto.ca/~cks/space/blog/unix/NoSwapConsequence)
Recently, Artem S. Tashkinov wrote on the Linux kernel mailing list about a Linux problem under memory pressure (via, and threaded here). The specific reproduction instructions involved having low RAM, turning off swap space, and then putting the system under load, and when that happened (emphasis mine):
Once you hit a situation when opening a new tab requires more RAM than is currently available, the system will stall hard. You will barely be able to move the mouse pointer. Your disk LED will be flashing incessantly (I'm not entirely sure why). [...]
I'm afraid I have bad news for the people snickering at Linux here; if you're running without swap space, you can probably get any Unix to behave this way under memory pressure. If you can't on your particular Unix, I'd actually say that your Unix is probably not letting you get full use out of your RAM.
To simplify a bit, we can divide pages of user memory up into anonymous pages and file-backed pages. File-backed pages are what they sound like; they come from some specific file on the filesystem that they can be written out to (if they're dirty) or read back in from. Anonymous pages are not backed by a file, so the only place they can be written out to and read back in from is swap space. Anonymous pages mostly come from dynamic memory allocations and from modifying the program's global variables and data; file backed pages come mostly from mapping files into memory with mmap() and also, crucially, from the code and read-only data of the program.
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Dsynth details on Dragonfly (https://www.dragonflydigest.com/2019/08/27/23398.html)
First, history: DragonFly has had binaries of dports available for download for quite some time. These were originally built using poudriere, and then using the synth tool put together by John Marino. Synth worked both to build all software in dports, and as a way to test DragonFly’s SMP capability under extreme load.
Matthew Dillon is working on a new version, called dsynth. It is available now but not yet part of the build. He’s been working quickly on it and there’s plenty more commits than what I have linked here. It’s already led to finding more high-load fixes.
dsynth
DSynth is basically synth written in C, from scratch. It is designed to give us a bulk builder in base and be friendly to porting and jails down the line (for now its uses chroot's).
The original synth was written by John R. Marino and its basic flow was used in writing this program, but as it was written in ada no code was directly copied.
The intent is to make dsynth compatible with synth's configuration files and directory structure.
This is a work in progress and not yet ready for prime-time. Pushing so we can get some more eyeballs. Most of the directives do not yet work (everything, and build works, and 'cleanup' can be used to clean up any dangling mounts).
dsynth code (https://gitweb.dragonflybsd.org/dragonfly.git/blob/HEAD:/usr.bin/dsynth/dsynth.1)
News Roundup
Instant Workstation (https://euroquis.nl/freebsd/2019/08/12/instant-workstation.html)
Some considerable time ago I wrote up instructions on how to set up a FreeBSD machine with the latest KDE Plasma Desktop. Those instructions, while fairly short (set up X, install the KDE meta-port, .. and that’s it) are a bit fiddly.
So – prompted slightly by a Twitter exchange recently – I’ve started a mini-sub-project to script the installation of a desktop environment and the bits needed to support it. To give it at least a modicum of UI, dialog(1) is used to ask for an environment to install and a d