VRAM and memory in DXVK: what the game sees and how to change it

Two kinds of “out of memory”

People use the phrase for two different problems. They look alike and have different fixes.

Upstream’s 3.0 notes say the new compiler reduced memory use in some 32-bit games, and that Direct3D 9 buffer uploads now use bounded memory; see DXVK 3.x. That helps with kind 2 but does not remove the limit.

See what your game is told

1. The game’s own settings screen. Many older games show the detected video memory, or refuse high settings when it looks too low.
2. The DXVK HUD. DXVK_HUD=memory shows how much memory DXVK itself is using (HUD page). It shows DXVK’s use, not what the game is told.
3. The log. At start-up DXVK prints the memory heaps of the GPU it found. On our Wine test machine, which has a software GPU, the log said:

          1
          info:  Memory:
          
          
          
        
          2
          info:    Heap 0: 15.70 GiB (DEVICE_LOCAL)
          
          
          A software GPU uses system RAM, so the "video" heap is about the size of the host’s memory. A real card shows its own VRAM here.
        

Direct3D 8 and 9 games: d3d9.maxAvailableMemory

The option sets the starting value, in megabytes, for Direct3D 9’s memory tracking and for what the game gets when it asks how much texture memory is available. The default is 4096.

d3d9.maxAvailableMemory = 2048

We got the same 2,038 MB on Windows and under Wine (F25). The default setting shows less than 4096 for a 32-bit program. We did not investigate why.

Raise or lower it only when a game misreads memory. Two related options exist: d3d9.textureMemory (default 100) is a budget of address space for mapped textures, and does not change quality or real memory use; d3d9.memoryTrackTest is a test mode that pairs with it. We did not test either, and the options reference marks both advanced.

Direct3D 10 and 11 games: dxgi.maxDeviceMemory

For these games the figure comes from DXGI. dxgi.maxDeviceMemory caps the dedicated memory reported, in megabytes, and dxgi.maxSharedMemory caps the shared (system) memory. Both default to 0, meaning no override.

dxgi.maxDeviceMemory = 4096

With 4096 a Direct3D 11 test program saw 4,096 MB of dedicated memory (F26). Without it our software GPU reported its real heap: about 16 GB because the lab machine has 16 GB of RAM it shares.

32-bit games and the 4 GB limit

A 32-bit program has a fixed amount of address space: 2 GB, or 4 GB if its executable is flagged Large Address Aware (LAA). The game’s code, its mods, DXVK and the graphics driver all live in that space. When it fills up, the game crashes with an out-of-memory error even though your graphics card has plenty free.

• Check the flag. The Game Checker reads the LAA flag from the exe header and says if a 32-bit program is not Large Address Aware. It reads the file only; it changes nothing.
• Some older games need a 4 GB patch. The community says Fallout: New Vegas does (our game database marks it as such); we cannot confirm that for any other title without reading its exe. Patching sets the flag.
• DXVK changes how tight it is. Issue 1318 (135 comments) is where users discuss 32-bit memory problems. We have not measured address-space use; upstream says 3.0 reduced memory use in some titles.

Memory budget and defragmentation (advanced)

Three DXVK-wide options deal with how DXVK manages memory. Leave them at default unless a game page tells you otherwise. We have not tested any of them.

• dxvk.maxMemoryBudget: a debug cap in megabytes on how much VRAM DXVK itself uses. Expect heavy slowdowns.
• dxvk.enableMemoryDefrag: allows defragmenting VRAM when memory is wasted or over budget. Auto skips drivers on a blocklist. A debug option.
• dxvk.zeroMappedMemory: clears freed mapped memory. A last resort for games that read uninitialised data, at a high CPU cost.

“VRAM leak” reports

Memory use that grows is not always a leak: drivers and DXVK cache things on purpose. To tell them apart, use the same scene, show DXVK_HUD=memory, and write down the figure every few minutes for half an hour. Flat after warm-up is caching; a steady climb is worth reporting. Put the HUD reading, the DXVK version and the log in the report; the error page shows how to read the log. We have not reproduced a leak ourselves.

Game recipes

These are the memory lines that apply to each game and the evidence behind them. None has been run in the game itself (why).

See also The Sims 3, GTA IV, Fallout: New Vegas and The Sims 2. For choosing which GPU a game sees, read GPU selection.