How to measure VAS with FSUIPC

measuring-vas-fsuipc2.pngYou can measure the status of the VAS using FSUIPC and place the measurement on screen.

If you don’t know what VAS is, please read first this post :: How Memory is Managed by the OS.
Further you can read all about Memory issues in this category.

With FSUIPC you can measure the Available FS memory (as it is called in the FSUIPC Offset Status.pdf). With the offset code 024C with Type S32 you measure the Available Virtual Address Space in kilobytes. This value is updated every 10 seconds.

The Available VAS + the Virtual Size of the process Prepar3D.exe equals ± 4GB as being the total VAS space for each 32 bits process. With other words: the  4GB VAS space minus the virtual size of the process Prepar3D.exe equals the remaining available virtual address space. When this VAS space is consumed…you get an OOM error message.vas-maxed-out2.png

How to show Available VAS on screen.

  1. In Prepar3D open Add-ons – FSUIPC and select tab Logging.
  2. Check: IPC reads  in Log Details and FS Window (or FS Title Bar) in Display to
  3. Fill Offset = 024C and Type =32 in the Specific value checks
  4. Close with OK
  5. You can drag and resize the green FS Window bar as desired to any convenient place on the screen. Once configured in FSUIPC it will appear again at next start.

measuring-vas-fsuipc.pngYou could also place the information in the FS Title Bar for a better reading result.

The value in the Title bar is read as 2643028 x KB=2.643 MB …as we speak of 2.6 GB.vas-maxed out3.PNG

How could you reach an OOM situation on startup?


In the image above you see the development of a coming OOM:: Out of Memory situation of the virtual address space. When a value of 4096 MB  (4GB) is reached, you get this message:vas-maxed-out2.png

How could you reach an OOM situation on startup?

start-scenario.pngThere are 2 possibilities for start after you have activated prepar3d.exe. Either the previous flight starts or the Prepar3D® Training Scenario Setup screen is activated.

When scrolling through the list of airplanes, textures are loaded. The texture map pages textures out if they have not been used in 10 seconds.  

Unfortunately, the timer used to age texture has not been initialized yet when the scenario start-up screen loads.  

The textures for the aircraft you looked at, but didn’t pick, will stay loaded until roughly 10 seconds after the simulation finishes loading.  This makes it much easier to run out of memory on startup.  

If you go to the vehicle select screen, after the sim is loaded up, the textures should page out ok while in the preview screen.  You can still have issues if you scroll too fast though because of the 10 second limit.  

For the next release, Update 2.5,  textures will page out in both versions of the vehicle select screen and the textures will page our much more quickly.

Issue is soved in V2.5

Source: Prepar3D®

How to prevent?

Select_vehicle-01.pngAt startup of the sim with the Prepar3D® Training Scenario Setup screen the virtual space is used for approx. 0.8 GB.

When scrolling through the list of airplanes with its different textures, each airplane will consume an amount of VAS.

At the moment you reach the 4GB limit you get the OOM error message.

If you won’t run the risk of OOM at startup, you could reduce the number of airplanes in the folder ../Simobjects/Airplanes, so you have little to choose (little to scroll) OR you start the sim with the Previous Flight which automatically runs at startup.

If you want to change the aircraft then, just go to Vehicles select screen and select the vehicle. You could also reduce the risk when you make a list of your Favorites. (Hit the asterix on the line of your choice and check the asterix “Show Only Favorites”).

According to Prepar3D® this should be improved in the next release.

If you want to watch the development of your VAS with FSUIPC click HERE to read how you can view on screen.