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model-saver : fix expert shared/chunk FFN length key clobber (#26693)

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The saver called add_kv with LLM_KV_EXPERT_SHARED_FEED_FORWARD_LENGTH twice, the
second time passing n_ff_chexp. gguf_set_val_u32 removes-then-appends, so the second
call clobbers the first: the saved shared_feed_forward_length ends up as n_ff_chexp
(0 for every arch except GroveMoE), and expert_chunk_feed_forward_length is never
written at all.

So a save->load roundtrip of any MoE model with a shared expert loses n_ff_shexp. On
reload the arch falls back to n_ff for the shexp tensor shape, that no longer matches
the saved tensor, and the model FAILS to load. Hits qwen2moe, qwen3-next, granite-moe,
hunyuan-moe, ernie4.5, bailingmoe2, nemotron-h, and the other shared-expert MoEs.

Fix: the second call writes LLM_KV_EXPERT_CHUNK_FEED_FORWARD_LENGTH.

test-llama-archs: set expert_shared_feed_forward_length to a value distinct from n_ff
in the MoE setup so the roundtrip exercises it. Without the fix the reload fails on a
shexp tensor-shape mismatch; with it, every arch roundtrips clean.
This commit is contained in:
Caleb DeLeeuw 2026-08-09 23:32:01 -07:00 • committed by GitHub
parent aea252fb4a
commit 0377426cef
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2 changed files with 2 additions and 1 deletions
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2
src/llama-model-saver.cpp
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@ -213,7 +213,7 @@ void llama_model_saver::add_kv_from_model() {
add_kv(LLM_KV_FEED_FORWARD_LENGTH, hparams.n_ff_arr, true);
add_kv(LLM_KV_EXPERT_FEED_FORWARD_LENGTH, hparams.n_ff_exp);
add_kv(LLM_KV_EXPERT_SHARED_FEED_FORWARD_LENGTH, hparams.n_ff_shexp);
add_kv(LLM_KV_EXPERT_SHARED_FEED_FORWARD_LENGTH, hparams.n_ff_chexp);
add_kv(LLM_KV_EXPERT_CHUNK_FEED_FORWARD_LENGTH, hparams.n_ff_chexp);
add_kv(LLM_KV_SWIGLU_CLAMP_EXP, hparams.swiglu_clamp_exp);
add_kv(LLM_KV_SWIGLU_CLAMP_SHEXP, hparams.swiglu_clamp_shexp);
add_kv(LLM_KV_USE_PARALLEL_RESIDUAL, hparams.use_par_res);

1
tests/test-llama-archs.cpp
View file

@ -217,6 +217,7 @@ static gguf_context_ptr get_gguf_ctx(const llm_arch arch, const bool moe) {
if (moe) {
ms.add_kv(LLM_KV_EXPERT_FEED_FORWARD_LENGTH, n_ff);
ms.add_kv(LLM_KV_EXPERT_SHARED_FEED_FORWARD_LENGTH, n_ff / 2); // distinct from n_ff so a saver key-clobber surfaces on reload
ms.add_kv(LLM_KV_INTERLEAVE_MOE_LAYER_STEP, uint32_t(2));
ms.add_kv(LLM_KV_EXPERT_COUNT, uint32_t(2));
ms.add_kv(LLM_KV_EXPERT_USED_COUNT, uint32_t(1));