Control on DBus-daemon virtual memory usage ballooning

[Hailun Tan]

After digging some past bug reports on D-Bus, I found the following one:

https://gitlab.freedesktop.org/dbus/dbus/-/issues/105

It mentioned that D-Bus never freed its data.

D-Bus authors, please advise whether the above statement  is true. If it is
not, please advise how to free D-Bus daemon data holdup?

On Mon, Sep 7, 2020 at 4:17 PM Hailun Tan <dearambermini at gmail.com> wrote:

> I am currently trying  the D-Bus sample codes from the following link:
>
> https://linoxide.com/how-tos/d-bus-ipc-mechanism-linux/
>
> It  worked.
>
> Then I performed the exhaustion tests on the sample code above i.e.,
> broadcast the DBus messages rapidly to other DBus users, who did not handle
> the received message as quick as the sender sent them, the D-Bus
> daemon's virtual memory usage started to grow, which  is expected as DBus
> daemon's outgoing queue accumulated.
>
> Then I stopped the sender process, the D-Bus daemon's virtual memory usage
> should start to shrink as the receiver is disseminating the message with
> the filter function. However, the D-Bus daemon's virtual memory usage did
> not shrink down even after the receiver process completed disseminating all
> the data.
>
> I have tried the above tests for  the following three cases:
>
> 1. sender application broadcasted the messages to all
> receiver applications via DBus.
> 2. sender application sent the method call messages to a
> particular receiver application, without requesting a reply
> 3.  sender application sent the method call messages to a
> particular receiver application, requesting a reply from receiver
> application.
>
> case 1 and 2 will make the dbus daemon virtual memory usage enlarge and
> its virtual memory usage would not shrink if the sender application were
> terminated and the receiver application completed the handlings of all
> messages from sender.
>
> Case 3, however, would not have the DBus daemon VM usage grown. The VM
> usage remained unchanged during the test.
>
> So my question is, how to make the case 1 and 2 behave as case 3? Or
> alternatively,  even though the VM usage grew due to the message queues in
> DBus daemon,  its VM usage should shrink down to its original state when
> the system was up?
>
> I doubted that DBus daemon should have some configurations to set so that
> it can release these memory usage after the receiver application completed
> handling these messages. I have spent quite a while looking for such a
> configuration in the DBus daemon config file (for session bus) in the
> following link:
>
> https://dbus.freedesktop.org/doc/dbus-daemon.1.html
>
> But I cannot find  any. So Please advise how I can make dbus daemon to
> release these VM usages after the messages have been handled?
>
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