Feature Request: Auto-detect encrypted volumes and disable mmap to prevent system freezes

[LifetimeVip]

Feature Idea

When running ComfyUI on a VeraCrypt-encrypted volume, loading large models (7GB+ safetensors checkpoints) causes severe system freezing or complete unresponsiveness.

Root cause analysis:

VeraCrypt's driver opens host files with FILE_NO_INTERMEDIATE_BUFFERING, completely bypassing the Windows file system cache. Meanwhile, ComfyUI defaults to memory-mapped file I/O (mmap) when loading safetensors via safetensors.safe_open(). The combination creates a catastrophic I/O pattern:

1. Every mmap page fault triggers a physical disk read through VeraCrypt's synchronous encryption pipeline (256KB fragments, XTS-AES decrypt on each)
2. VeraCrypt's I/O pipeline threads run at LOW_REALTIME_PRIORITY, starving normal-priority threads (Python/UI)
3. With no OS cache, repeated accesses to the same tensor data cause repeated physical reads

A 7GB model creates ~28,000 fragmented reads through the encryption layer. The system appears frozen because VeraCrypt's real-time threads consume all available CPU for AES operations while the UI/compute threads can't schedule.

The existing --disable-mmap flag fixes this (line 174 in cli_args.py, used at line 137 in comfy/utils.py). When mmap is disabled, safetensors are loaded eagerly as CPU tensors (sequential large reads), which work efficiently with VeraCrypt's read-ahead cache.

However, --disable-mmap requires user manual discovery. The fix should be automatic.

Suggested implementation:

1. Auto-detect encrypted volumes: At startup, check if the model directory resides on a volume opened with FILE_NO_INTERMEDIATE_BUFFERING or other encryption indicators.

2. Fall back gracefully: When an encrypted or no-cache volume is detected, automatically treat --disable-mmap as enabled, or print a prominent warning suggesting the user enable it.

3. Simpler alternative: Change the default of --disable-mmap to True on Windows, or at minimum print a startup warning about potential issues with encrypted volumes.

Existing Solutions

The --disable-mmap CLI flag already exists. The comfy/utils.py line 137-138 shows:

if DISABLE_MMAP:
    tensor = tensor.to(device=device, copy=True)

There is also a TODO comment: "# TODO: Not sure if this is the best way to bypass the mmap issues".

Other

I have analyzed both VeraCrypt's source code (veracrypt/VeraCrypt, specifically src/Driver/EncryptedIoQueue.c and src/Driver/Ntvol.c) and ComfyUI's model loading path (comfy/utils.py, comfy/memory_management.py, comfy/model_management.py) to arrive at this root cause analysis.

@comfyanonymous

[rattus128]

We just merged #13802 that changes the game completely with mmaps. Please try with your encrypted disk setup and let us know.

[brendanhoar]

@LifetimeVip - thanks for the work here. I'm in the same boat, veracrypt and comfyui model loading constantly giving performance issues. Let us know if #13802 sorted things out, did nothing or introduced more issues. Again, thanks to you both, @rattus128 and @LifetimeVip for working on this stuff.

B

[samaduddin083-afk]

basic:

models:

• model: [name of the model]
  url: [url of the source, e.g. https://huggingface.co/...]
  paths: [list of paths to the model]

  • path: [path to the model]
  • path: [path to the model]
    hashes: [hashes for the model]
  • hash: [hash]
    type: [AutoV1, AutoV2, SHA256, CRC32, and Blake3]
    type: [type of the model, e.g. diffuser, lora, etc.]

• model:
  ...

compatible with ComfyUI-Manager's .yaml snapshot

custom_nodes:
comfyui: [commit hash]
file_custom_nodes:

• disabled: [bool]
  filename: [.py filename]
  ...
  git_custom_nodes:
  [git-url]:
  disabled: [bool]
  hash: [commit hash]
  ...

[samaduddin083-afk]

basic:

models:

• model: [name of the model]
  url: [url of the source, e.g. https://huggingface.co/...]
  paths: [list of paths to the model]

  • path: [path to the model]
  • path: [path to the model]
    hashes: [hashes for the model]
  • hash: [hash]
    type: [AutoV1, AutoV2, SHA256, CRC32, and Blake3]
    type: [type of the model, e.g. diffuser, lora, etc.]

• model:
  ...

compatible with ComfyUI-Manager's .yaml snapshot

custom_nodes:
comfyui: [commit hash]
file_custom_nodes:

• disabled: [bool]
  filename: [.py filename]
  ...
  git_custom_nodes:
  [git-url]:
  disabled: [bool]
  hash: [commit hash]
  ...