Syncthing uses too much RAM (killed by oom_reaper)

[bitey29]

One of my systems (let’s call it “Q”) has 3GB RAM. It ran Syncthing just fine for months. A few days ago I’ve added a new device “N” to a big folder (500k files, 1.5k folders, 45GiB) that was previously only shared between “Q” & “L”. “Q” is configured as my introducer. “L” has 32GB RAM, “N” has 16GB - So I don’t see any issues on those.

Is there a way to constraint the memory usage of Syncthing in a way that prevents the system to become unresponsive for many minutes before the oom-killer kicks in and forces Syncthing to restart?

[calmh (Jakob Borg)]

You can use some of the tuning options to reduce memory usage, and you can set GOMEMLIMIT to set a limit for how much the runtime should allocate: Configuration Tuning — Syncthing documentation

[bitey29]

This looks like a good guide for my situation:

Optimising Syncthing for low end hardware

First of all, I know that many topics have been created to discuss the question of running Syncthing on low end / slow / old devices, and I have done my part to search and study them. The problem is that the vast majority were support related, and are thus locked now, with no further discussion possible. Nevertheless, I apologise if I ask questions or raise subjects that have already been discussed to death. I have Syncthing installed on a few older devices. The slowest of them has the followin…

I did find “Max Concurrent Incoming Request Ki B” under Advanced → Options which I guess is the same as the mentioned maxConcurrentIncomingRequestKiB and set it to 32768.

I guess for the other’s I’ll have to find where the Debian packager has put the config file in the filesystem..

UPDATE: Is this the right file? /home/syncthing/.config/syncthing/config.xml

UPDATE2: I believe it is, since it contains this which is not the default value: <maxConcurrentIncomingRequestKiB>32768</maxConcurrentIncomingRequestKiB>

[calmh (Jakob Borg)]

All the things are editable in the advanced dialog, except GOMEMLIMIT etc which are environment variables.

[bitey29]

Okey, so to set one of those

• STNORESTART=1
• GOGC=25
• GOMEMLIMIT=??

I need to make systemd pass those as environment variables?

[calmh (Jakob Borg)]

If systemd is how you start Syncthing, yes, that sounds about right.

[bitey29]

what unit is GOMEMLIMIT use? bytes? KiB? MiB? MB?

UPDATE: It seems it want’s a String that includes the unit. So I’ve added those lines:

Environment="STNORESTART=1"
Environment="GOMEMLIMIT=1GiB"

to /lib/systemd/system/syncthing@.service.

Let’s see how that behaves.

[bitey29]

Changing all those settings helped! No more out-of-memory problems. I’ve actually lightened them up again by increasing maxFolderConcurrency from the suggested value 1 up to 2 because it annoyed me that it stopped handling all other folders when one large change requires long transfer times.

[Martchus]

@bitey29

to /lib/systemd/system/syncthing@.service.

Just a side-note: You can also use a drop-in configuration for this, e.g. using systemctl edit syncthing@.service.