New responsibilities

As part of the same process outlined in Matthias Clasen's "LibreOffice packages" email, my management chain has made the decision to stop all upstream and downstream work on desktop Bluetooth, multimedia applications (namely totem, rhythmbox and sound-juicer) and libfprint/fprintd. The rest of my upstream and downstream work will be reassigned depending on Red Hat's own priorities (see below), as I am transferred to another team that deals with one of a list of Red Hat’s priority projects.

I'm very disappointed, because those particular projects were already starved for resources: I spent less than 10% of my work time on them in the past year, with other projects and responsibilities taking most of my time.

This means that, in the medium-term at least, all those GNOME projects will go without a maintainer, reviewer, or triager:

- gnome-bluetooth (including Settings panel and gnome-shell integration)

- totem, totem-pl-parser, gom

- libgnome-volume-control

- libgudev

- geocode-glib

- gvfs AFC backend

Those freedesktop projects will be archived until further notice:

- power-profiles-daemon

- switcheroo-control

- iio-sensor-proxy

- low-memory-monitor

I will not be available for reviewing libfprint/fprintd, upower, grilo/grilo-plugins, gnome-desktop thumbnailer sandboxing patches, or any work related to XDG specifications.

Kernel work, reviews and maintenance, including recent work on SteelSeries headset and Logitech devices kernel drivers, USB revoke for Flatpak Portal support, or core USB is suspended until further notice.

All my Fedora packages were orphaned about a month and a half ago, it's likely that there are still some that are orphaned, if there are takers. RHEL packages were unassigned about 3 weeks ago, they've been reassigned since then, so I cannot point to the new maintainer(s).

If you are a partner, or a customer, I would recommend that you get in touch with your Red Hat contacts to figure out what the plan is going forward for the projects you might be involved with.

If you are a colleague that will take on all or part of the 90% of the work that's not being stopped, or a community member that was relying on my work to further advance your own projects, get in touch, I'll do my best to accommodate your queries, time permitting.

I'll try to make sure to update this post, or create a new one if and when any of the above changes.

GMemoryMonitor (low-memory-monitor, 2nd phase)

TL;DR

Use GMemoryMonitor in glib 2.63.3 and newer in your applications to lower overall memory usage, and detect low memory conditions.

low-memory-monitor

To start with, let's come back to low-memory-monitor, announced at the end of August.

It's not really a “low memory monitor”. I know, the name is deceiving, but it actually monitors memory pressure stalls, and how hard it is for the kernel to allocate memory when applications need it. The longer it takes to allocate memory, the longer the kernel takes to allocate it, usually because it needs to move memory around to make room for a big allocation, when an application starts up for example, or prepares an in-memory buffer for saving.

It is not a daemon that will kill programs on low memory. It's not a user-space out-of-memory killer, and does not take those policy decisions. It can however be configured to ask the kernel to do that. The kernel doesn't really know what it's doing though, and user-space isn't helping either, so best disable that for now...

As listed in low-memory-monitor's README (and in the announcement post), there were a number of similar projects around, but none that would offer everything we needed, eg.:

• Has a D-Bus interface to propagate low memory conditions
• Requires Linux 5.2's kernel memory pressure stalls information (Android's lowmemorykiller daemon has loads of code to get the same information from the kernel for older versions, and it really is quite a lot of code)
• Written in a compiled language to save on startup/memory usage costs (around 500 lines of C code, as counted by sloccount)
• Built-in policy, based upon values used in Android and Endless OS

 GMemoryMonitor

Next up, in our effort to limit memory usage, we'll need some help from applications. That's where GMemoryMonitor comes in. It's simple enough, listen to the low-memory-warning signal and free some image thumbnails, index caches, or dump some data to disk, when you receive a signal.

The signal also gives you a “warning level”, with 255 being when low-memory-monitor would trigger the kernel's OOM killer, and lower values different levels of “try to be a good citizen”.

The more astute amongst you will have noticed that low-memory-monitor runs as root, on the system bus, and wonder how those new fangled (5 years old today!) sandboxed applications would receive those signals. Fear not! Support for a portal version of GMemoryMonitor landed in xdg-desktop-portal on the same day as in glib. Everything tied together with installed tests that use the real xdg-desktop-portal to test the portal and unsandboxed versions.

How about an OOM killer?

By using memory pressure stall information, we receive information about the state of the kernel before getting into swapping that'd cause the machine to become unusable. This also means that, as our threshold for keeping everything ticking is low, if we were to kill high memory consumers, we'd get a butter smooth desktop, but, based on my personal experience, your browser and your mail client would take it in turns disappearing from your desktop in a way that you wouldn't even notice.

We'll definitely need to think about our next step in application state management, and changing our running applications paradigm.

Distributions should definitely disable the OOM killer for now, and possibly try their hands at upstream some systemd OOMPolicy and OOMScoreAdjust options for system daemons.

Conclusion

Creating low-memory-monitor was easy enough, getting everything else in place was decidedly more complicated. In addition to requiring changes to glib, xdg-desktop-portal and python-dbusmock, it also required a lot of work on the glib CI to save me from having to write integration tests in C that would have required a lot of scaffolding. So thanks to all involved in particular Philip Withnall for his patience reviewing my changes.

low-memory-monitor: new project announcement

I'll soon be flying to Greece for GUADEC but wanted to mention one of the things I worked on the past couple of weeks: the low-memory-monitor project is off the ground, though not production-ready.

low-memory-monitor, as its name implies, monitors the amount of free physical memory on the system and will shoot off signals to interested user-space applications, usually session managers, or sandboxing helpers, when that memory runs low, making it possible for applications to shrink their memory footprints before it's too late either to recover a usable system, or avoid taking a performance hit.

It's similar to Android's lowmemorykiller daemon, Facebook's oomd, Endless' psi-monitor, amongst others

Finally a GLib helper and a Flatpak portal are planned to make it easier for applications to use, with an API similar to iOS' or Android's.

Combined with work in Fedora to use zswap and remove the use of disk-backed swap, this should make most workstation uses more responsive and enjoyable.