OpenGL Application makes Xorg leaks

Question

I am working on a rather big Qt5/OpenGL application. Each time the application run and exit on a linux with nvidia driver, with a compositor active, nvidia-smi shows an increase of 4Mb of VRAM usage for Xorg process.

My suposition would be that even if my application leaks, everything should be released when it is destroyed, but it does not seems to be the case.

On this thread OpenGL GPU Memory cleanup, required?, Someone mentionned that it would not be the case if "Display list" are shared.

I do not know much about OpenGL, and could not find coherent informations about this issue on the web.

My objective is to understand how this could happen, where it may come from in my code and how to fix it.

Note :

The leaks are present in Xorg after my Aplication is stopped and no other process then Xorg and Desktop Environnement related are shown in nvidia-smi

The DE I use does not matter (tested : KDE, Lxde, OpenBox, Gnome, Unity).

The Linux Distribution I use (almost) does not matter (tested: Ubuntu 16.04, Ubuntu 18.04, fedora 26) (not reproduced on ArchLinux yet, we are still investigating this)

The nvidia driver version does not matter, tested 340, 384, 390.

Just to get the insidious *"argh, why didn't I notice that?"* out of the way: Are you sure, your process *actually* terminates? It often happens that one forgets to actually terminate the main event loop/process, despite the last window being closed. — datenwolf, Jul 01 '18 at 11:56
I have updated my questions. Leaks disappear if compositor is not active — Mathieu Westphal, Jul 01 '18 at 13:40

score 0 · Accepted Answer · answered Jul 12 '18 at 07:12

0

The issue was resolved thanks to an intense debugging session.

The leak was caused by NULL parenting the parent of the windowContainer containing the QVTKOpenGLWindow just before deletion.

This code was here before when we used a QOpenGLWidget and it caused no issue. In any case, NULL parenting a widget before deletion is useless so removing the line resolve the issue.

This leak shouldn't happen though, even in this situation, so I have opened a Qt issue to report it.

answered Jul 12 '18 at 07:12

Mathieu Westphal

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I don't understand why you are setting that widget's parent to NULL at all. – rubenvb Jul 12 '18 at 07:22
No idea, another dev did it in 2009, maybe Qt4 related ? That's all I know. In any case there is no reason to do that so removing it fix the issue. – Mathieu Westphal Jul 12 '18 at 07:51

OpenGL Application makes Xorg leaks

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