Three chained bugs that made Z-Image (and other GGUF DiTs) crash at generation
on anything but a huge, fully-idle GPU. Verified end to end on an RTX 6000 Ada:
Q2_K now plans resident and generates a real 1024x1024 PNG on both the resident
and forced-group-offload paths.
- Memory planner over-estimated the GGUF transformer's resident size. diffusers
keeps GGUF weights PACKED (uint8 GGUFParameter) and dequantises per-matmul
transiently, so resident VRAM is ~= the on-disk size, not the unpacked bf16
size (measured: Q2_K 3.64->3.68 GiB, Q8_0 7.22->7.25 GiB). The old per-quant
expansion (x8 for Q2) over-estimated ~7.6x, so a 3.6 GB model on a 48 GB-free
card was judged a "tight fit" and forced into group offload. Replace the
multiplier table with estimate_gguf_resident_mib = storage * 1.05 (matches
diffusers' own get_memory_footprint of a loaded GGUF model).
- torch.compile with fullgraph=True crashed under CPU offload: group/model/
sequential offload installs a @torch.compiler.disable'd ModuleGroup.onload_
hook, which graph-breaks. Drop fullgraph when offloading is planned, same as
the existing step-cache case (fullgraph = not (cache_active or offload_active)).
This mirrors diffusers' documented compile+offload guidance.
- compile_repeated_blocks compiles one graph per distinct block shape, but
Z-Image's "repeated" blocks are heterogeneous (~11 variants), above dynamo's
default recompile_limit of 8, so a resident load hard-errored under fullgraph.
Raise the limit (diffusers' documented fix for regional-compile recompilation).
Confirmed force_parameter_static_shapes=False is the wrong lever: same variant
count, ~6x slower compile.
Also drops the now-dead infer_gguf_quant_label / gguf_filename plumbing and adds
regression tests for the estimate and the offload fullgraph drop.
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