llama : adjust default context size + print warnings#10136
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ngxson
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Nov 2, 2024
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Thanks! This should prevent me from burning my swapfile whenever I forget to specify -c
Tested and it shows the log too:
> ./llama-cli -m ../models/Meta-Llama-3.1-8B-Instruct-Q4_K_M.gguf -cnv -p "You are a helpful assistant"
...
llama_new_context_with_model: n_ctx_per_seq (4096) < n_ctx_train (131072) -- the full capacity of the model will not be utilized
...
slaren
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Nov 2, 2024
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Is 4096 a good value, or should we go lower? |
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According to HF hub statistics, the most used model nowadays is the llama 3 (3.1, 3.2) 8B With a context size of 4096, the KV takes around 512MB which I think is a very reasonable amount. |
arthw
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Nov 15, 2024
* llama : adjust default context size + print warnings ggml-ci * ggml-ci : add missing gpu-layers + adjust context sizes
arthw
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* llama : adjust default context size + print warnings ggml-ci * ggml-ci : add missing gpu-layers + adjust context sizes
pestopoppa
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Since PR ggml-org#16653 (Dec 15, 2025), the default n_ctx is 0 to enable automatic GPU memory fitting. This causes llama-lookup and llama-lookahead to crash when run without explicit -c flag: GGML_ASSERT(batch.seq_id[batch.n_tokens] && "llama_batch size exceeded") Root cause: Both examples use params.n_ctx directly for batch initialization, but params.n_ctx remains 0 even after the context is properly initialized to n_ctx_train internally. Bug history: - Nov 2023: lookahead.cpp created (PR ggml-org#4207) with params.n_ctx pattern - Dec 2023: lookup.cpp created (PR ggml-org#4484) with same pattern - Nov 2024: default n_ctx changed to 4096 (PR ggml-org#10136) - bug dormant - Dec 2025: default n_ctx changed to 0 (PR ggml-org#16653) - bug activated The bug was dormant for 2+ years because params.n_ctx defaulted to 512, then 4096. PR ggml-org#16653 changed it to 0 for GPU auto-fitting, triggering the crash. Fix: Use llama_n_ctx(ctx) to get the actual runtime context size, matching the pattern already used elsewhere in lookup.cpp (line 72) and in speculative.cpp/speculative-simple.cpp. Tested: llama-lookup now works without -c flag (12.5% acceptance on Gemma-3-1B). Note: llama-lookahead has a separate pre-existing issue with sequence initialization (n_seq_max=1 vs W+G+1 needed) that is unrelated to this fix.
pestopoppa
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Since PR ggml-org#16653 (Dec 15, 2025), the default n_ctx is 0 to enable automatic GPU memory fitting. This causes llama-lookup and llama-lookahead to crash when run without explicit -c flag: GGML_ASSERT(batch.seq_id[batch.n_tokens] && "llama_batch size exceeded") Root cause: Both examples use params.n_ctx directly for batch initialization, but params.n_ctx remains 0 even after the context is properly initialized to n_ctx_train internally. Bug history: - Nov 2023: lookahead.cpp created (PR ggml-org#4207) with params.n_ctx pattern - Dec 2023: lookup.cpp created (PR ggml-org#4484) with same pattern - Nov 2024: default n_ctx changed to 4096 (PR ggml-org#10136) - bug dormant - Dec 2025: default n_ctx changed to 0 (PR ggml-org#16653) - bug activated The bug was dormant for 2+ years because params.n_ctx defaulted to 512, then 4096. PR ggml-org#16653 changed it to 0 for GPU auto-fitting, triggering the crash. Fix: Use llama_n_ctx(ctx) to get the actual runtime context size, matching the pattern already used elsewhere in lookup.cpp (line 72) and in speculative.cpp/speculative-simple.cpp. Tested: llama-lookup now works without -c flag (12.5% acceptance on Gemma-3-1B). Note: llama-lookahead has a separate pre-existing issue with sequence initialization (n_seq_max=1 vs W+G+1 needed) that is unrelated to this fix.
ggerganov
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Jan 30, 2026
* lookup, lookahead: fix crash when n_ctx not specified Since PR #16653 (Dec 15, 2025), the default n_ctx is 0 to enable automatic GPU memory fitting. This causes llama-lookup and llama-lookahead to crash when run without explicit -c flag: GGML_ASSERT(batch.seq_id[batch.n_tokens] && "llama_batch size exceeded") Root cause: Both examples use params.n_ctx directly for batch initialization, but params.n_ctx remains 0 even after the context is properly initialized to n_ctx_train internally. Bug history: - Nov 2023: lookahead.cpp created (PR #4207) with params.n_ctx pattern - Dec 2023: lookup.cpp created (PR #4484) with same pattern - Nov 2024: default n_ctx changed to 4096 (PR #10136) - bug dormant - Dec 2025: default n_ctx changed to 0 (PR #16653) - bug activated The bug was dormant for 2+ years because params.n_ctx defaulted to 512, then 4096. PR #16653 changed it to 0 for GPU auto-fitting, triggering the crash. Fix: Use llama_n_ctx(ctx) to get the actual runtime context size, matching the pattern already used elsewhere in lookup.cpp (line 72) and in speculative.cpp/speculative-simple.cpp. Tested: llama-lookup now works without -c flag (12.5% acceptance on Gemma-3-1B). Note: llama-lookahead has a separate pre-existing issue with sequence initialization (n_seq_max=1 vs W+G+1 needed) that is unrelated to this fix. * lookahead: fix n_seq_max and kv_unified configuration Lookahead decoding requires: - W + G + 1 = 31 sequences for parallel Jacobi decoding - Unified KV cache for coupled sequences in batch splitting These requirements were broken after PR #14482 changed validation logic. Consolidates fix from PR #18730 per maintainer request. Commit message drafted with Claude.
4b1tQu4ntN3k0
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Feb 2, 2026
* lookup, lookahead: fix crash when n_ctx not specified Since PR ggml-org#16653 (Dec 15, 2025), the default n_ctx is 0 to enable automatic GPU memory fitting. This causes llama-lookup and llama-lookahead to crash when run without explicit -c flag: GGML_ASSERT(batch.seq_id[batch.n_tokens] && "llama_batch size exceeded") Root cause: Both examples use params.n_ctx directly for batch initialization, but params.n_ctx remains 0 even after the context is properly initialized to n_ctx_train internally. Bug history: - Nov 2023: lookahead.cpp created (PR ggml-org#4207) with params.n_ctx pattern - Dec 2023: lookup.cpp created (PR ggml-org#4484) with same pattern - Nov 2024: default n_ctx changed to 4096 (PR ggml-org#10136) - bug dormant - Dec 2025: default n_ctx changed to 0 (PR ggml-org#16653) - bug activated The bug was dormant for 2+ years because params.n_ctx defaulted to 512, then 4096. PR ggml-org#16653 changed it to 0 for GPU auto-fitting, triggering the crash. Fix: Use llama_n_ctx(ctx) to get the actual runtime context size, matching the pattern already used elsewhere in lookup.cpp (line 72) and in speculative.cpp/speculative-simple.cpp. Tested: llama-lookup now works without -c flag (12.5% acceptance on Gemma-3-1B). Note: llama-lookahead has a separate pre-existing issue with sequence initialization (n_seq_max=1 vs W+G+1 needed) that is unrelated to this fix. * lookahead: fix n_seq_max and kv_unified configuration Lookahead decoding requires: - W + G + 1 = 31 sequences for parallel Jacobi decoding - Unified KV cache for coupled sequences in batch splitting These requirements were broken after PR ggml-org#14482 changed validation logic. Consolidates fix from PR ggml-org#18730 per maintainer request. Commit message drafted with Claude.
shaofeiqi
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Feb 6, 2026
* lookup, lookahead: fix crash when n_ctx not specified Since PR ggml-org#16653 (Dec 15, 2025), the default n_ctx is 0 to enable automatic GPU memory fitting. This causes llama-lookup and llama-lookahead to crash when run without explicit -c flag: GGML_ASSERT(batch.seq_id[batch.n_tokens] && "llama_batch size exceeded") Root cause: Both examples use params.n_ctx directly for batch initialization, but params.n_ctx remains 0 even after the context is properly initialized to n_ctx_train internally. Bug history: - Nov 2023: lookahead.cpp created (PR ggml-org#4207) with params.n_ctx pattern - Dec 2023: lookup.cpp created (PR ggml-org#4484) with same pattern - Nov 2024: default n_ctx changed to 4096 (PR ggml-org#10136) - bug dormant - Dec 2025: default n_ctx changed to 0 (PR ggml-org#16653) - bug activated The bug was dormant for 2+ years because params.n_ctx defaulted to 512, then 4096. PR ggml-org#16653 changed it to 0 for GPU auto-fitting, triggering the crash. Fix: Use llama_n_ctx(ctx) to get the actual runtime context size, matching the pattern already used elsewhere in lookup.cpp (line 72) and in speculative.cpp/speculative-simple.cpp. Tested: llama-lookup now works without -c flag (12.5% acceptance on Gemma-3-1B). Note: llama-lookahead has a separate pre-existing issue with sequence initialization (n_seq_max=1 vs W+G+1 needed) that is unrelated to this fix. * lookahead: fix n_seq_max and kv_unified configuration Lookahead decoding requires: - W + G + 1 = 31 sequences for parallel Jacobi decoding - Unified KV cache for coupled sequences in batch splitting These requirements were broken after PR ggml-org#14482 changed validation logic. Consolidates fix from PR ggml-org#18730 per maintainer request. Commit message drafted with Claude.
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fix #8817, #9563 (comment)
By default, the examples will use a context size of 4096, instead of the training context of the model. In a lot of cases, the default training context can be very big - 32k to 128k tokens, which causes enormous KV cache allocation and failures for regular hardware.
Also, add warning logs when the specified context size per sequence does not match the training context.