🚧 compressive transformer

labml_nn/transformers/compressive/__init__.py

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+from typing import Optional, List
+
+import torch
+import torch.nn.functional as F
+from torch import nn
+
+from labml_helpers.module import Module, TypedModuleList
+from labml_nn.transformers.feed_forward import FeedForward
+from labml_nn.transformers.mha import PrepareForMultiHeadAttention
+from labml_nn.transformers.xl.relative_mha import RelativeMultiHeadAttention
+from labml_nn.utils import clone_module_list
+
+
+class Conv1dCompression(Module):
+    def __init__(self, compression_ratio: int, d_model: int):
+        super().__init__()
+        self.conv = nn.Conv1d(d_model, d_model, kernel_size=compression_ratio, stride=compression_ratio)
+
+    def forward(self, mem: torch.Tensor):
+        """
+        * `mem` has shape `[seq_len, batch, d_model]`
+        """
+
+        # Change the dimensions of `mem` so that we can run it through the convolution layer.
+        # The convolution layer accepts in the form `[batch, features, sequence]`
+        mem = mem.permute(1, 2, 0)
+        # Get compressed memory
+        c_mem = self.conv(mem)
+        # Permute back to form `[seq_len, batch, d_model]`
+        return c_mem.permute(2, 0, 1)
+
+
+class CompressiveTransformerLayer(Module):
+    def __init__(self, *,
+                 d_model: int,
+                 self_attn: RelativeMultiHeadAttention,
+                 feed_forward: FeedForward,
+                 dropout_prob: float,
+                 compress: Conv1dCompression):
+        """
+        * `d_model` is the token embedding size
+        * `self_attn` is the [self attention module](relative_mha.html)
+        * `feed_forward` is the feed forward module
+        * `dropout_prob` is the probability of dropping out after self attention and FFN
+        """
+        super().__init__()
+        self.compress = compress
+        self.size = d_model
+        self.self_attn = self_attn
+        self.feed_forward = feed_forward
+        self.dropout = nn.Dropout(dropout_prob)
+        self.norm_self_attn = nn.LayerNorm([d_model])
+        self.norm_ff = nn.LayerNorm([d_model])
+
+    def with_memory(self, z: torch.Tensor, mem: Optional[torch.Tensor], c_mem: Optional[torch.Tensor]):
+        if mem is None:
+            return z
+
+        if c_mem is not None:
+            mem = torch.cat((c_mem, mem), dim=0)
+
+        mem = self.norm_self_attn(mem)
+        return torch.cat((mem, z), dim=0)
+
+    def forward(self, *,
+                x: torch.Tensor,
+                mem: Optional[torch.Tensor],
+                c_mem: Optional[torch.Tensor],
+                mask: torch.Tensor):
+        """
+        * `x` are the token level feature vectors of shape `[seq_len, batch_size, d_model]`
+        * `mem` are the past token level feature vectors of shape `[mem_len + c_mem_len * c, batch_size, d_model]`
+        * `mask` is a matrix of shape `[seq_len, c_mem_len + mem_len + seq_len, batch_size]` or `[seq_len, c_mem_len + mem_len + seq_len, 1]`.
+        `mask[i, j]` is  true if token at `i` can see token at `j`.
+        """
+
+        # Normalize the vectors before doing self attention
+        z = self.norm_self_attn(x)
+        m_z = self.with_memory(z, mem, c_mem)
+        # Attention
+        self_attn = self.self_attn(query=z, key=m_z, value=m_z, mask=mask)
+        # Add the attention results
+        x = x + self.dropout(self_attn)
+
+        # Normalize for feed-forward
+        z = self.norm_ff(x)
+        # Pass through the feed-forward network
+        ff = self.feed_forward(z)
+        # Add the feed-forward results back
+        x = x + self.dropout(ff)
+
+        #
+        return x
+
+
+class CompressiveTransformer(Module):
+    """
+    ## Transformer XL Model
+
+    This consists of multiple transformer XL layers
+    """
+
+    def __init__(self, layer: CompressiveTransformerLayer, n_layers: int):
+        super().__init__()
+        # Make copies of the transformer layer
+        self.layers = clone_module_list(layer, n_layers)
+        # Final normalization layer
+        self.norm = nn.LayerNorm([layer.size])
+
+    def forward(self, x: torch.Tensor, mem: List[torch.Tensor], c_mem: List[torch.Tensor], mask: torch.Tensor):
+        """
+        * `x` are the token embeddings vectors of shape `[seq_len, batch_size, d_model]`
+        * `mem` are the past token level feature vectors of shape `[mem_len, batch_size, d_model]`  for each layer
+        * `mask` is the masking matrix
+        """
+        # List to store token level feature vectors,
+        # which will be the memories for the next sequential batch.
+        new_mem = []
+        # Run through each transformer layer
+        for i, layer in enumerate(self.layers):
+            # Add to the list of feature vectors
+            new_mem.append(x.detach())
+            # Memory
+            m = mem[i] if mem else None
+            # Memory
+            cm = c_mem[i] if c_mem else None
+            # Run through the transformer XL layer
+            x = layer(x=x, mem=m, c_mem=cm, mask=mask)
+        # Finally, normalize the vectors
+        return self.norm(x), new_mem
+
+
+class AttentionReconstructionLoss:
+    def __init__(self, layers: TypedModuleList[CompressiveTransformerLayer]):
+        self.layers = layers
+        self.loss_func = nn.MSELoss()
+
+    def prepare_for_attn(self, pmha: PrepareForMultiHeadAttention, x: torch.Tensor):
+        head_shape = x.shape[:-1]
+
+        # Linear transform
+        weight = pmha.linear.weight.detach()
+        bias = pmha.linear.bias.detach() if pmha.linear.bias is not None else None
+        x = F.linear(x, weight, bias)
+
+        # Split last dimension into heads
+        x = x.view(*head_shape, pmha.heads, pmha.d_k)
+
+        # Output has shape `[seq_len, batch_size, heads, d_k]` or `[batch_size, d_model]`
+        return x
+
+    def attn(self, layer: RelativeMultiHeadAttention, query: torch.Tensor, key: torch.Tensor, value: torch.Tensor):
+        query = self.prepare_for_attn(layer.query, query)
+        key = self.prepare_for_attn(layer.key, key)
+        value = self.prepare_for_attn(layer.value, value)
+
+        # Compute attention scores $Q K^\top$.
+        # This gives a tensor of shape `[seq_len, seq_len, batch_size, heads]`.
+        scores = torch.einsum('ibhd,jbhd->ijbh', query, key)
+
+        # Scale scores $\frac{Q K^\top}{\sqrt{d_k}}$
+        scores *= layer.scale
+
+        # $softmax$ attention along the key sequence dimension
+        # $\underset{seq}{softmax}\Bigg(\frac{Q K^\top}{\sqrt{d_k}}\Bigg)$
+        attn = layer.softmax(scores)
+
+        # Multiply by values
+        # $$\underset{seq}{softmax}\Bigg(\frac{Q K^\top}{\sqrt{d_k}}\Bigg)V$$
+        return torch.einsum("ijbh,jbhd->ibhd", attn, value)
+
+    def calc_loss(self, layer: CompressiveTransformerLayer, h: torch.Tensor, mem: torch.Tensor):
+        h = h.detach()
+        mem = mem.detach()
+
+        c_mem = layer.compress(mem)
+
+        return self.loss_func(self.attn(layer.self_attn, h, mem, mem),
+                              self.attn(layer.self_attn, h, c_mem, c_mem))
+
+    def __call__(self, h: List[torch.Tensor], mem: List[torch.Tensor]):
+        losses = [self.calc_loss(layer, h[n], mem[n]) for n, layer in enumerate(self.layers)]
+        return sum(losses)

labml_nn/transformers/compressive/experiment.py

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+"""
+---
+title: Compressive Transformer Experiment
+summary: This experiment trains a compressive transformer model on tiny Shakespeare dataset.
+---
+
+# Compressive Transformer Experiment
+
+This is an annotated PyTorch experiment to train a compressive transformer model.
+"""
+from typing import List, Tuple, NamedTuple
+
+import torch
+import torch.nn as nn
+
+from labml import experiment, tracker, monit, logger
+from labml.configs import option
+from labml.logger import Text
+from labml_helpers.metrics.simple_state import SimpleStateModule
+from labml_helpers.module import Module
+from labml_helpers.train_valid import BatchIndex, hook_model_outputs
+from labml_nn.experiments.nlp_autoregression import NLPAutoRegressionConfigs
+from labml_nn.transformers.compressive import CompressiveTransformer, AttentionReconstructionLoss, \
+    CompressiveTransformerLayer, Conv1dCompression
+
+
+class CompressedMemory(NamedTuple):
+    mem: List[torch.Tensor]
+    c_mem: List[torch.Tensor]
+
+
+class AutoregressiveModel(Module):
+    """
+    ## Auto regressive model
+    """
+
+    def __init__(self, n_vocab: int, d_model: int, transformer: CompressiveTransformer):
+        super().__init__()
+        # Token embedding module
+        self.src_embed = nn.Embedding(n_vocab, d_model)
+        # Transformer
+        self.transformer = transformer
+        # Final layer
+        self.generator = nn.Linear(d_model, n_vocab)
+        # Masks
+        self.mask_x = None
+        self.mask_mem = None
+
+    def forward(self, x: torch.Tensor, mem: CompressedMemory):
+        # Length of the memory
+        if mem is not None:
+            mem, c_mem = mem.mem, mem.c_mem
+        else:
+            mem = []
+            c_mem = []
+
+        m_len = len(mem[0]) if mem else 0
+        if c_mem:
+            m_len += len(c_mem[0])
+
+        # Create a subsequent mask for tokens
+        if self.mask_x is None or self.mask_x.shape[0] < len(x):
+            from labml_nn.transformers.utils import subsequent_mask
+            self.mask_x = subsequent_mask(len(x)).to(x.device)
+        # Create an all ones (full visibility) mask for memory
+        if self.mask_mem is None or self.mask_mem.shape[1] < m_len or self.mask_mem.shape[0] < len(x):
+            self.mask_mem = self.mask_x.new_ones(len(x), m_len, 1)
+
+        # Concatenate the masks if there is memory
+        if m_len:
+            mask = torch.cat((self.mask_mem[:len(x), :m_len], self.mask_x[:len(x), :len(x)]), dim=1)
+        # Use the subsequent mask otherwise
+        else:
+            mask = self.mask_x[:len(x), :len(x)]
+
+        # Token embeddings
+        x = self.src_embed(x)
+        # Run it through the transformer
+        res, mem = self.transformer(x, mem, c_mem, mask)
+        # Generate logits of the next token
+        res = self.generator(res)
+        #
+        return res, mem
+
+
+class Configs(NLPAutoRegressionConfigs):
+    """
+    ## Configurations
+
+    The default configs can and will be over-ridden when we start the experiment
+    """
+
+    model: AutoregressiveModel
+
+    # Token embedding size
+    d_model: int = 128
+    # Number of attention heads
+    heads: int = 4
+    # Dropout probability
+    dropout: float = 0.0
+    # Number of features in FFN hidden layer
+    d_ff: int = 256
+    # Number of transformer layers
+    n_layers: int = 6
+    # Number of memories to keep
+    mem_len: int = 8
+    # State module to maintain memories when switching between training and validation
+    memory = SimpleStateModule()
+    # Attention Reconstruction Loss
+    attention_reconstruction_loss: AttentionReconstructionLoss
+    # Compression ratio
+    compression_ratio: int = 4
+    # Compressed memory length
+    c_mem_len: int = 128
+
+    def init(self):
+        # Set tracker configurations
+        tracker.set_scalar("accuracy.*", True)
+        tracker.set_scalar("loss.*", True)
+        tracker.set_scalar("ar_loss.*", False)
+        # Add a hook to log module outputs
+        hook_model_outputs(self.mode, self.model, 'model')
+        # This will keep the accuracy metric stats and memories separate for training and validation.
+        self.state_modules = [self.accuracy, self.memory]
+
+    @torch.no_grad()
+    def merge_memory(self, mem: CompressedMemory, new_mem: List[torch.Tensor]) \
+            -> Tuple[CompressedMemory, List[torch.Tensor]]:
+        """
+        Concatenate memories and remove old memories to keep a maximum of
+        `mem_len` memories.
+        """
+
+        # If it's configured not to use memory
+        if self.mem_len == 0:
+            return CompressedMemory([], []), []
+
+        if mem is not None:
+            mem, c_mem = mem.mem, mem.c_mem
+        else:
+            mem, c_mem = [], []
+        # Concatenate with old memory
+        if mem:
+            mem = [torch.cat((m, x), dim=0) for m, x in zip(mem, new_mem)]
+        else:
+            mem = new_mem
+
+        if len(mem[0]) > self.mem_len:
+            n_c_mem = (len(mem[0]) - self.mem_len + self.compression_ratio - 1) // self.compression_ratio
+            old_mem = []
+            trunc_mem = []
+            for m in mem:
+                n_old = n_c_mem * self.compression_ratio
+                cm, m = torch.split(m, [n_old, len(m) - n_old])
+                old_mem.append(cm)
+                trunc_mem.append(m)
+            mem = trunc_mem
+
+            new_c_mem = []
+            for i, layer in enumerate(self.model.transformer.layers):
+                new_c_mem.append(layer.compress(old_mem[i]))
+
+            if c_mem:
+                c_mem = [torch.cat((m, nm), dim=0) for m, nm in zip(c_mem, new_c_mem)]
+            else:
+                c_mem = new_c_mem
+
+            # Truncate old memories
+            if len(c_mem[0]) > self.c_mem_len:
+                c_mem = [m[-self.c_mem_len:] for m in c_mem]
+        else:
+            old_mem = []
+
+        #
+        return CompressedMemory(mem, c_mem), old_mem
+
+    def step(self, batch: any, batch_idx: BatchIndex):
+        """
+        ### Training/validation step
+        """
+
+        # Move data to the device
+        data, target = batch[0].to(self.device), batch[1].to(self.device)
+
+        # Update global step (number of tokens processed) when in training mode
+        if self.mode.is_train:
+            tracker.add_global_step(data.shape[0] * data.shape[1])
+
+        # Whether to capture model outputs
+        with self.mode.update(is_log_activations=batch_idx.is_last):
+            # Get memories
+            mem = self.memory.get()
+            # Run the model
+            output, new_mem = self.model(data, mem)
+            # Merge memory
+            mem, old_mem = self.merge_memory(mem, new_mem)
+            # Update memories
+            self.memory.set(mem)
+
+        # Calculate and log cross entropy loss
+        loss = self.loss_func(output, target)
+        tracker.add("loss.", loss)
+
+        if old_mem:
+            ar_loss = self.attention_reconstruction_loss(new_mem, old_mem)
+            tracker.add("ar_loss.", ar_loss)
+            # loss = loss + ar_loss
+
+        # Calculate and log accuracy
+        self.accuracy(output, target)
+        self.accuracy.track()
+
+        # Train the model
+        if self.mode.is_train:
+            # Calculate gradients
+            loss.backward()
+            # Clip gradients
+            torch.nn.utils.clip_grad_norm_(self.model.parameters(), max_norm=self.grad_norm_clip)
+            # Take optimizer step
+            self.optimizer.step()
+            # Log the model parameters and gradients on last batch of every epoch
+            if batch_idx.is_last:
+                tracker.add('model', self.model)
+            # Clear the gradients
+            self.optimizer.zero_grad()
+
+        # Save the tracked metrics
+        tracker.save()
+
+    def sample(self):
+        """
+        ### Sampling function to generate samples periodically while training
+        """
+
+        # Starting prompt
+        prompt = self.prompt
+        # Collect output for printing
+        log = [(prompt, Text.subtle)]
+        # memory
+        mem = CompressedMemory([], [])
+        # Sample 25 tokens
+        for i in monit.iterate('Sample', 25):
+            # Tokenize the prompt
+            data = self.text.text_to_i(prompt).unsqueeze(-1)
+            # Move to device
+            data = data.to(self.device)
+            # Get the model output
+            output, new_mem = self.model(data, mem)
+            # Get the model prediction (greedy)
+            output = output.argmax(dim=-1).squeeze(1)
+            # Add the prediction to prompt
+            prompt += self.prompt_separator + self.text.itos[output[-1]]
+            # Only feed the last character to model in next iteration, rest will go in as memories
+            prompt = prompt[-1:]
+            # Add the prediction for logging
+            log += [(self.prompt_separator + self.text.itos[output[-1]], Text.value)]
+            # Update memory
+            mem, _ = self.merge_memory(mem, new_mem)
+
+        # Print the sampled output
+        logger.log(log)
+
+
+@option(Configs.model)
+def autoregressive_model(c: Configs):
+    """
+    ### Initialize the auto-regressive model
+    """
+    from labml_nn.transformers.xl import RelativeMultiHeadAttention
+    from labml_nn.transformers.feed_forward import FeedForward
+    m = AutoregressiveModel(c.n_tokens, c.d_model, CompressiveTransformer(
+        CompressiveTransformerLayer(d_model=c.d_model,
+                                    self_attn=RelativeMultiHeadAttention(c.heads, c.d_model, c.dropout),
+                                    feed_forward=FeedForward(c.d_model, c.d_ff, c.dropout),
+                                    dropout_prob=c.dropout,
+                                    compress=Conv1dCompression(c.compression_ratio, c.d_model)), c.n_layers))
+    return m.to(c.device)
+
+
+@option(Configs.attention_reconstruction_loss)
+def attention_reconstruction_loss(c: Configs):
+    """
+    ### Initialize the auto-regressive model
+    """
+    return AttentionReconstructionLoss(c.model.transformer.layers)
+
+
+def main():
+    """
+    ### Run the experiment
+    """
+    # Create experiment
+    experiment.create(name="compressive_transformer", comment='')
+    # Create configs
+    conf = Configs()
+    # Load configurations
+    experiment.configs(conf,
+                       # A dictionary of configurations to override
+                       {'tokenizer': 'character',
+                        'text': 'tiny_shakespeare',
+                        'optimizer.learning_rate': 2.5e-4,
+                        'optimizer.optimizer': 'AdamW',
+                        'prompt': 'It is',
+                        'prompt_separator': '',
+
+                        'train_loader': 'sequential_train_loader',
+                        'valid_loader': 'sequential_valid_loader',
+
+                        'seq_len': 8,
+                        'mem_len': 8,
+                        'epochs': 128,
+                        'batch_size': 32,
+                        'inner_iterations': 25,
+                        })
+
+    # Set models for saving and loading
+    experiment.add_pytorch_models({'model': conf.model})
+
+    # Start the experiment
+    with experiment.start():
+        # `TrainValidConfigs.run`
+        conf.run()
+
+
+#
+if __name__ == '__main__':
+    main()