optimize VRAM for calculating pos_bias in LayoutLM v2, v3 #26139
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What does this PR do?
The current implementation of calculating 1d_pos_bias/2d_pos_bias in LayoutLMv2, v3 is VRAM-consuming due to the large one-hot matrix.
Considering the idea of 1d_pos_bias/2d_pos_bias is to categorize all relative positions into several buckets, assign each position id to a specific bucket based on its relative distance to another token, and embed the position id into a feature, we can drop the large one-hot matrix and directly use the Linear weight features like an nn.Embedding.
In my tests, as for an input sequence of$[10, 1024]$ (bz, nseq), this can save 3 Gb VRAM for 2d_pos_bias calculations
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Who can review?
@ArthurZucker and @younesbelkada