[Model] factoring out MambaMixer out of Jamba (#8993)

Signed-off-by: mzusman <mor.zusmann@gmail.com>

Author: mzusman

vllm/model_executor/layers/mamba/mamba_mixer.py

@@ -0,0 +1,217 @@
+import torch
+from torch import nn
+from torch.nn.parameter import Parameter
+
+from vllm.attention.backends.abstract import AttentionMetadata
+from vllm.distributed.parallel_state import (
+    get_tensor_model_parallel_rank, get_tensor_model_parallel_world_size)
+from vllm.model_executor.custom_op import CustomOp
+from vllm.model_executor.layers.layernorm import RMSNorm
+from vllm.model_executor.layers.linear import (ColumnParallelLinear,
+                                               MergedColumnParallelLinear,
+                                               RowParallelLinear)
+from vllm.model_executor.layers.mamba.ops.causal_conv1d import (
+    causal_conv1d_fn, causal_conv1d_update)
+from vllm.model_executor.layers.mamba.ops.mamba_ssm import (
+    selective_scan_fn, selective_state_update)
+from vllm.model_executor.models.mamba_cache import MambaCacheParams
+from vllm.model_executor.utils import set_weight_attrs
+
+
+# Adapted from transformers.models.mamba.modeling_mamba.MambaMixer
+@CustomOp.register("mamba_mixer")
+class MambaMixer(CustomOp):
+    """
+    Compute ∆, A, B, C, and D the state space parameters and compute
+    the `contextualized_states`. A, D are input independent
+    (see Mamba paper [1] Section 3.5.2 "Interpretation of A"
+    for why A isn't selective) ∆, B, C are input-dependent
+    (this is a key difference between Mamba and the linear time
+    invariant S4, and is why Mamba is called
+    **selective** state spaces)
+    """
+
+    def __init__(self,
+                 hidden_size: int,
+                 ssm_state_size: int,
+                 conv_kernel_size: int,
+                 intermediate_size: int,
+                 time_step_rank: int,
+                 use_conv_bias: bool,
+                 use_bias: bool,
+                 use_rms_norm: bool,
+                 rms_norm_eps: float = 1e-5,
+                 activation="silu"):
+        super().__init__()
+        self.time_step_rank = time_step_rank
+        self.ssm_state_size = ssm_state_size
+        self.use_rms_norm = use_rms_norm
+        self.activation = activation
+
+        self.conv1d = ColumnParallelLinear(
+            input_size=conv_kernel_size,
+            output_size=intermediate_size,
+            bias=use_conv_bias,
+        )
+        # unsqueeze to fit conv1d weights shape into the linear weights shape.
+        # Can't do this in `weight_loader` since it already exists in
+        # `ColumnParallelLinear` and `set_weight_attrs`
+        # doesn't allow to override it
+        self.conv1d.weight.data = self.conv1d.weight.data.unsqueeze(1)
+
+        self.in_proj = MergedColumnParallelLinear(hidden_size,
+                                                  [intermediate_size] * 2,
+                                                  bias=use_bias)
+        # selective projection used to make dt, B and C input dependent
+        self.x_proj = RowParallelLinear(
+            intermediate_size,
+            time_step_rank + ssm_state_size * 2,
+            bias=False,
+        )
+        # time step projection (discretization) -
+        # In the forward we need to apply dt_proj without the bias,
+        # as the bias is added in the selective scan kernel.
+        self.dt_proj = ColumnParallelLinear(time_step_rank,
+                                            intermediate_size,
+                                            bias=True,
+                                            skip_bias_add=True)
+
+        def weight_loader(param: Parameter, loaded_weight: torch.Tensor):
+            tp_rank = get_tensor_model_parallel_rank()
+            tp_size = get_tensor_model_parallel_world_size()
+            param.data.copy_(
+                loaded_weight.data.split(loaded_weight.shape[0] // tp_size,
+                                         dim=0)[tp_rank])
+
+        def A_weight_loader(param: Parameter, loaded_weight: torch.Tensor):
+            weight_loader(param, -torch.exp(loaded_weight.float()))
+
+        tp_size = get_tensor_model_parallel_world_size()
+        self.A = nn.Parameter(
+            torch.empty(
+                intermediate_size // tp_size,
+                ssm_state_size,
+                dtype=torch.float32,
+            ))
+        self.D = nn.Parameter(torch.ones(intermediate_size // tp_size))
+
+        set_weight_attrs(self.D, {"weight_loader": weight_loader})
+        set_weight_attrs(self.A, {"weight_loader": A_weight_loader})
+
+        self.out_proj = RowParallelLinear(
+            intermediate_size,
+            hidden_size,
+            bias=use_bias,
+            input_is_parallel=True,
+        )
+
+        self.dt_layernorm = RMSNorm(time_step_rank,
+                                    eps=rms_norm_eps) if use_rms_norm else None
+
+        self.b_layernorm = RMSNorm(ssm_state_size,
+                                   eps=rms_norm_eps) if use_rms_norm else None
+
+        self.c_layernorm = RMSNorm(ssm_state_size,
+                                   eps=rms_norm_eps) if use_rms_norm else None
+
+    def forward_native(self, hidden_states: torch.Tensor,
+                       attn_metadata: AttentionMetadata,
+                       conv_state: torch.Tensor, ssm_state: torch.Tensor):
+        pass
+
+    def forward_cuda(self, hidden_states: torch.Tensor,
+                     attn_metadata: AttentionMetadata,
+                     mamba_cache_params: MambaCacheParams):
+
+        # 1. Gated MLP's linear projection
+        projected_states = self.in_proj(hidden_states)[0].transpose(-2, -1)
+        hidden_states, gate = projected_states.chunk(2, dim=-2)
+
+        # 2. Convolution sequence transformation
+        conv_weights = self.conv1d.weight.view(self.conv1d.weight.size(0),
+                                               self.conv1d.weight.size(2))
+
+        if attn_metadata.query_start_loc is not None \
+            and attn_metadata.context_lens_tensor is not None:
+            # |---------- N-1 iteration --------|
+            # |---------------- N iteration ---------------------|
+            # |- tokenA -|......................|-- newTokens ---|
+            # |---------- context_len ----------|
+            # |-------------------- seq_len ---------------------|
+            #                                   |-- query_len ---|
+            hidden_states = causal_conv1d_fn(
+                hidden_states,
+                conv_weights,
+                self.conv1d.bias,
+                activation=self.activation,
+                conv_states=mamba_cache_params.conv_state,
+                has_initial_state=attn_metadata.context_lens_tensor > 0,
+                cache_indices=mamba_cache_params.state_indices_tensor,
+                query_start_loc=attn_metadata.query_start_loc)
+        else:
+            hidden_states = causal_conv1d_update(
+                hidden_states.transpose(0, 1),
+                mamba_cache_params.conv_state,
+                conv_weights,
+                self.conv1d.bias,
+                self.activation,
+                conv_state_indices=mamba_cache_params.state_indices_tensor)
+            hidden_states = hidden_states.transpose(0, 1)
+
+        # 3. State Space Model sequence transformation
+        # 3.a. input varying initialization of time_step, B and C
+        ssm_parameters = self.x_proj(hidden_states.transpose(-2, -1))[0]
+
+        time_step, B, C = torch.split(
+            ssm_parameters,
+            [self.time_step_rank, self.ssm_state_size, self.ssm_state_size],
+            dim=-1,
+        )
+        if self.use_rms_norm:
+            assert self.dt_layernorm is not None
+            assert self.b_layernorm is not None
+            assert self.c_layernorm is not None
+            time_step = self.dt_layernorm(time_step.contiguous())
+            B = self.b_layernorm(B.contiguous())
+            C = self.c_layernorm(C.contiguous())
+
+        discrete_time_step = self.dt_proj(time_step)[0].transpose(-2, -1)
+        # 3.c perform the recurrence y ← SSM(A, B, C)(x)
+        time_proj_bias = (self.dt_proj.bias.float() if hasattr(
+            self.dt_proj, "bias") else None)
+
+        if attn_metadata.query_start_loc is not None \
+            and attn_metadata.context_lens_tensor is not None:
+            scan_outputs = selective_scan_fn(
+                hidden_states,
+                mamba_cache_params.ssm_state,
+                discrete_time_step,
+                self.A,
+                B.transpose(-2, -1),
+                C.transpose(-2, -1),
+                self.D.float(),
+                gate,
+                time_proj_bias,
+                delta_softplus=True,
+                cache_indices=mamba_cache_params.state_indices_tensor,
+                has_initial_state=attn_metadata.context_lens_tensor > 0,
+                query_start_loc=attn_metadata.query_start_loc)
+        else:
+            scan_outputs = selective_state_update(
+                mamba_cache_params.ssm_state,
+                hidden_states.transpose(0, 1),
+                discrete_time_step.transpose(0, 1),
+                self.A,
+                B,
+                C,
+                self.D,
+                gate.transpose(0, 1),
+                time_proj_bias,
+                dt_softplus=True,
+                state_batch_indices=mamba_cache_params.state_indices_tensor)
+            scan_outputs = scan_outputs.transpose(0, 1)
+
+        # 4. Final linear projection
+        contextualized_states = self.out_proj(scan_outputs.transpose(-2,
+                                                                     -1))[0]
+        return contextualized_states