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Michael Mayer 28eb11d468 TensorFlow: Trigger explicit GC to free C-allocated tensor memory #5394 
Signed-off-by: Michael Mayer <michael@photoprism.app>
2025-12-23 12:06:26 +01:00
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gc.go
image.go
image_test.go
info.go
info_test.go
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README.md
tensor_builder.go
tensorflow.go
util.go

README.md

PhotoPrism — TensorFlow Package

Last Updated: December 23, 2025

Overview

internal/ai/tensorflow provides the shared TensorFlow helpers used by PhotoPrism’s built-in AI features (labels, NSFW, and FaceNet embeddings). It wraps SavedModel loading, input/output discovery, image tensor preparation, and label handling so higher-level packages can focus on domain logic.

Key Components

  • Model Loading — SavedModel, GetModelTagsInfo, and GetInputAndOutputFromSavedModel discover and load SavedModel graphs with appropriate tags.
  • Input Preparation — Image, ImageTransform, and ImageTensorBuilder convert JPEG images to tensors with the configured resolution, color order, and resize strategy.
  • Output Handling — AddSoftmax can insert a softmax op when a model exports logits.
  • Labels — LoadLabels loads label lists for classification models.

Model Loading Notes

  • Built-in models live under assets/models/ and are accessed via helpers in internal/ai/vision and internal/ai/classify.
  • When a model lacks explicit tags or signatures, the helpers attempt to infer input/output operations. Logs will show when inference kicks in.
  • Classification models may emit logits; if ModelInfo.Output.Logits is true, a softmax op is injected at load time.

Memory & Garbage Collection

TensorFlow tensors are allocated in C memory and freed by Go GC finalizers in the TensorFlow bindings. Long-running inference can therefore show increasing RSS even when the Go heap is small. PhotoPrism periodically triggers garbage collection to return freed C-allocated tensor buffers to the OS. Control this behavior with:

  • PHOTOPRISM_TF_GC_EVERY (default 200, 0 disables).
    Lower values reduce peak RSS but increase GC overhead and can slow indexing.

Troubleshooting Tips

  • Model fails to load: Verify the SavedModel path, tags, and that saved_model.pb plus variables/ exist under assets/models/<name>.
  • Input/output mismatch: Check logs for inferred inputs/outputs and confirm vision.yml overrides (name, resolution, and TensorFlow.Input/Output).
  • Unexpected probabilities: Ensure logits are handled correctly and labels match output indices.
  • High memory usage: Confirm PHOTOPRISM_TF_GC_EVERY is set appropriately; model weights remain resident for the life of the process by design.

Related Docs