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Fix memory explosion on Apple Silicon #76

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Merged
TheTom merged 1 commit into from
Apr 14, 2026
Merged

Fix memory explosion on Apple Silicon #76

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10 changes: 6 additions & 4 deletions ggml/src/ggml-metal/ggml-metal-ops.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2838,10 +2838,12 @@ size_t ggml_metal_op_flash_attn_ext_extra_tmp(const ggml_tensor * op) {
res += ggml_type_size(GGML_TYPE_F32)*(ne01_max*ne02*ne03*nwg*(ne20 + 2));
}

// TurboFlash two-pass: always reserve partial result buffer to avoid graph reallocations
// partial_out: float[n_bh * n_blocks * dv]
// partial_ms: float[n_bh * n_blocks * 2] (max + sum per block)
{
// TurboFlash two-pass temp is only needed when the TurboFlash path is eligible.
// Reserving it unconditionally can massively inflate graph scratch usage for
// large-context models even when the normal FA path is selected.
if (ggml_metal_op_flash_attn_ext_use_turbo_flash(op)) {
// partial_out: float[n_bh * n_blocks * dv]
// partial_ms: float[n_bh * n_blocks * 2] (max + sum per block)
const int64_t n_bh = ne01 * ne02 * ne03;
const int64_t ne11 = op->src[1]->ne[1]; // T_kv
const int64_t n_blocks = (ne11 + 63) / 64; // ceil(T_kv / 64)
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