Wednesday, July 11, 2012

Xvfb Memory Leak Workaround

I've been using Xvfb, the X virtual frame buffer, for a few projects. Xvfb allows you to run applications that require a display, without actually having a graphics card or a screen. I started noticing that the resident memory used by the Xvfb process would continually go up. I could literally run processes that connect to the display in a loop and watch the memory grow. Clearly, there was some kind of memory leak going on.

I finally found a workaround to preventing this memory issue. If you add -noreset to the argument of Xvfb, the memory issue vanishes. By default, when the last client to Xvfb disconnects, the server resets itself. My guess is that this works fine when video memory is backed by a hardware device, but Xvfb has a bug where it doesn't free the memory it allocated for the buffer. By setting the noreset option, the server no longer restarts and the memory isn't lost.

Here's my Xvfb command line:
Xvfb :1 -screen 0 1024x768x24 -ac +extension GLX +render -noreset

An explanation of the other arguments:

  • :1 - Runs the server on "display 1". Most X servers run on display 0 by default.
  • -screen 0 1024x768x24 - Sets screen 0 (the default screen) to a resolution of 1024x768 with 24 bits per pixel.
  • -ac - Disables access control because X access control is incredibly painful to get right, and since the server is usually only accessible from localhost, it's not a big deal.
  • +extension GLX - Enables the OpenGL extension, allowing graphics programs that use OpenGL to work inside the virtual display.
  • +render - Enables the X Rendering extension, enabling advanced image compositing features that most applications will need.
I also use a simple Xvfb start script. It's available as a gist.

12 comments:

  1. Thanks that helped me out!

    -Mike

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  2. Well work!Thanks

    ReplyDelete
  3. Hi Jeff, good blog!

    I tell him that I tried to run the service with the parameter "-noreset", also without, and in all cases the memory grows indefinitely, the only way I found is to stop and restart the program running.

    I run it as follows: Xvfb :1 -screen 0 1x1x24 -dpi 96 -noreset &

    For more information, run Vvfb process, then export the DISPLAY variable and finally start an instance of tomcat over Ubuntu.

    I searched and tried, but still can not find any solution to this problem.

    Can guide me what else I can try?

    Thank you very much.

    ReplyDelete
  4. If you run Xvfb with -noreset, start the tomcat server, let the memory grow, and then kill the tomcat server, does the Xvdb memory go back down?

    If so, then there is a memory leak in tomcat, not Xvfb.

    ReplyDelete
  5. thanks for replying,

    I tell him that to stop the tomcat, xvfb memory remains the same, is not released.
    I'm thinking it may be a problem in the coding, and not in freeing the resources used (is an application made ​​with Java and SWT).

    ReplyDelete
  6. How do you do multiple extensions? Like +extension RANDR GLX? Also I'm using xvfb-run. How would you convert the Xvfb command to xvfb-run?

    ReplyDelete
    Replies
    1. Because I'm currently getting this error: Xlib: extension "RANDR" missing on display ":1". When running xvfb-run. Even when I use something like: xvfb-run --auto-servernum --server-num=1 --server-args="-noreset +extension RANDR" slimerjs robot.js

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