[feat] Adding Visual Attention

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Four blocksparsity layouts from DeepSpeed [#320]
 - Support several initialization options [#312]
 - Conv2DFeedforward feedforward part [#321]
+- VisualAttention [#329]
 
 
 ## [0.0.11] - 2022-05-30

README.md

@@ -167,6 +167,9 @@ Patrick et al., 2021](https://arxiv.org/abs/2106.05392)*
 - [2D Pooling](xformers/components/attention/pooling.py)
   - *[Metaformer is actually what you need for vision, Yu et al.](https://arxiv.org/pdf/2111.11418v1.pdf)*
 
+- [Visual Attention](xformers/components/attention/visual.py)
+  - *[`Visual Attention Network`_, Guo et al](https://arxiv.org/pdf/2202.09741.pdf)*
+
 - ... add a new one [see Contribution.md](CONTRIBUTING.md)
 
 </p></details>
@@ -199,7 +202,7 @@ Patrick et al., 2021](https://arxiv.org/abs/2106.05392)*
 
 <details><summary>Initializations </summary><p>
   This is completely optional, and will only occur when generating full models through xFormers, not when picking parts individually.
-  
+
   There are basically two initialization mechanisms exposed, but the user is free to initialize weights as he/she sees fit after the fact.
   - Parts can expose a `init_weights()` method, which define sane defaults
   - xFormers supports [specific init schemes](xformers/factory/weight_init.py) which *can take precedence* over the init_weights()

examples/cifarMetaformer.py

@@ -31,6 +31,7 @@ def __init__(
         num_classes=10,
         dim=384,
         attention="scaled_dot_product",
+        feedforward="MLP",
         layer_norm_style="pre",
         use_rotary_embeddings=True,
         linear_warmup_ratio=0.1,
@@ -45,8 +46,7 @@ def __init__(
         # Generate the skeleton of our hierarchical Transformer
 
         # This is a small poolformer configuration, adapted to the small CIFAR10 pictures (32x32)
-        # Any other related config would work,
-        # and the attention mechanisms don't have to be the same across layers
+        # Any other related config would work, and the attention mechanisms don't have to be the same across layers
         base_hierarchical_configs = [
             BasicLayerConfig(
                 embedding=64,
@@ -121,8 +121,8 @@ def forward(self, x):
 
     # Adjust batch depending on the available memory on your machine.
     # You can also use reversible layers to save memory
-    REF_BATCH = 512
-    BATCH = 512  # lower if not enough GPU memory
+    REF_BATCH = 768
+    BATCH = 256  # lower if not enough GPU memory
 
     MAX_EPOCHS = 50
     NUM_WORKERS = 4
@@ -172,6 +172,7 @@ def forward(self, x):
         num_classes=num_classes,
         attention="scaled_dot_product",
         layer_norm_style="pre",
+        feedforward="MLP",
         use_rotary_embeddings=True,
     )
     trainer = pl.Trainer(

tests/test_attentions.py

@@ -27,14 +27,16 @@
 )
 
 BATCH = 2
-SEQ = 128 if torch.cuda.is_available() else 32
+SEQ = 128 if torch.cuda.is_available() else 36
 MODEL = 128 if torch.cuda.is_available() else 16
 GLOBAL_ATTENTION_RATIO = (
     _DENSITY_THRESHOLD * 0.9
 )  # Make sure that we test the sparse implementation, no matter the threshold
 
 assert ATTENTION_REGISTRY.keys(), "Attention layers should have been registered"
 
+_non_order_invariant_attentions = ["visual", "pooling"]
+
 
 def _get_multihead(
     attention_name,
@@ -93,7 +95,9 @@ def noop(x):
 @pytest.mark.parametrize("residual_dropout", [0.0, 0.1])
 @pytest.mark.parametrize("causal", [True, False])
 @pytest.mark.parametrize("heads", [1, 4])
-@pytest.mark.parametrize("attention_name", ATTENTION_REGISTRY.keys())
+@pytest.mark.parametrize(
+    "attention_name", ATTENTION_REGISTRY.keys() - _non_order_invariant_attentions
+)
 @pytest.mark.parametrize("device", DEVICES)
 def test_order_invariance(
     attention_name: str,
@@ -104,9 +108,6 @@ def test_order_invariance(
     device: torch.device,
 ):
 
-    if int(math.sqrt(SEQ)) ** 2 != SEQ and attention_name == "pooling":
-        pytest.skip(f"{attention_name} requires squared sequence lengths")
-
     torch.manual_seed(42)
     torch.cuda.manual_seed_all(42)
 
@@ -120,6 +121,12 @@ def test_order_invariance(
         use_seperate_proj_weights=False,
     )
 
+    if (
+        int(math.sqrt(SEQ)) ** 2 != SEQ
+        and multi_head.attention.requires_squared_context
+    ):
+        pytest.skip(f"{attention_name} requires squared sequence lengths")
+
     # Check that a shuffled input produces the same results
     seqs = [SEQ, SEQ // 2] if (attention_name != "blocksparse") else [SEQ]
 
@@ -304,12 +311,15 @@ def test_broadcast_batch_dimension(
     device: torch.device,
     batch_sizes: Tuple[int, int, int],
 ):
-    if int(math.sqrt(SEQ)) ** 2 != SEQ and attention_name == "pooling":
-        pytest.skip(f"{attention_name} requires squared sequence lengths")
-
     Q_BATCH, K_BATCH, V_BATCH = batch_sizes
     multi_head = _get_multihead(attention_name, 0.0, 0.0, False, heads, device)
 
+    if (
+        int(math.sqrt(SEQ)) ** 2 != SEQ
+        and multi_head.attention.requires_squared_context
+    ):
+        pytest.skip(f"{attention_name} requires squared sequence lengths")
+
     if multi_head.attention.requires_same_k_q_dimensions:
         # pyre-fixme[29]: The library function `pytest.skip` is not supported by Pyre.
         pytest.skip(f"{attention_name} does not support different k, q dimensions yet.")
@@ -388,14 +398,20 @@ def test_torch_script_ability(
     heads: int,
     attn_dropout: float,
 ):
-    if attention_name in {"favor", "global", "local", "random", "pooling"}:
+    if attention_name in {"favor", "global", "local", "random"}:
         # pyre-fixme[29]: The library function `pytest.skip` is not supported by Pyre.
         pytest.skip(f"{attention_name} does not support scripting yet.")
 
     device = torch.device("cpu")
 
     multi_head = _get_multihead(attention_name, attn_dropout, 0.0, False, heads, device)
 
+    if (
+        int(math.sqrt(SEQ)) ** 2 != SEQ
+        and multi_head.attention.requires_squared_context
+    ):
+        pytest.skip(f"{attention_name} requires squared sequence lengths")
+
     # input for tracing the function
     q = torch.rand((BATCH, SEQ, MODEL), device=device)
     k = torch.rand((BATCH, SEQ, MODEL), device=device)

xformers/components/attention/base.py

@@ -53,6 +53,9 @@ def __init__(self, dropout: Optional[float] = None, *args, **kwargs):
         # so that the MHA wrapper should skip it
         self.requires_skip_multi_head = False
 
+        # This attention requires a context length which is squared, often due to 2D pooling
+        self.requires_squared_context = False
+
         # Whether this attention mechanism supports attention masks
         self.supports_attention_mask = True
         self.supports_key_padding_mask = False

xformers/components/attention/pooling.py

@@ -62,6 +62,10 @@ def __init__(
         # This operator does not really handle q,k,v
         self.requires_same_k_q_dimensions = True
 
+        # This attention requires the 2d structure out of the context,
+        # implictly assumed to be a squared length
+        self.requires_squared_context = True
+
     def forward(self, q: torch.Tensor, *_, **__):
         # Expose the 2D token structure
         B, HW, C = q.shape

xformers/components/attention/visual.py

@@ -0,0 +1,96 @@
+# Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.
+#
+# This source code is licensed under the BSD license found in the
+# LICENSE file in the root directory of this source tree.
+
+
+import math
+from dataclasses import dataclass
+
+import torch
+import torch.nn as nn
+
+from xformers.components.attention import Attention, AttentionConfig, register_attention
+
+
+@dataclass
+class VisualAttentionConfig(AttentionConfig):
+    dim_model: int  # dimension of the input sequence
+
+
+class LKA(nn.Module):
+    def __init__(self, dim: int):
+        super().__init__()
+        self.conv0 = nn.Conv2d(dim, dim, 5, padding=2, groups=dim)
+        self.conv_spatial = nn.Conv2d(
+            dim, dim, 7, stride=1, padding=9, groups=dim, dilation=3
+        )
+        self.conv1 = nn.Conv2d(dim, dim, 1)
+
+    def forward(self, x: torch.Tensor):
+        u = x.clone()
+        attn = self.conv0(x)
+        attn = self.conv_spatial(attn)
+        attn = self.conv1(attn)
+
+        return u * attn
+
+
+@register_attention("visual", VisualAttentionConfig)
+class Visual(Attention):
+    def __init__(
+        self,
+        dim_model: int,
+        *_,
+        **__,
+    ):
+        """
+        Large kernel attention mechanism, as proposed in `Visual Attention Network`_, Guo et al (2022).
+        The original notation is tentatively kept as is. See https://github.com/Visual-Attention-Network
+        for the reference implementation
+
+        .. Note: compared to the paper, this block contains the LKA (Large Kernel Attention)
+            and the prior and posterior transformations (Conv2d and activation)
+
+        .. _`Visual Attention Network` : https://arxiv.org/pdf/2202.09741.pdf
+        """
+        super().__init__()
+
+        self.block = nn.Sequential(
+            nn.Conv2d(dim_model, dim_model, 1),
+            nn.GELU(),
+            LKA(dim_model),
+            nn.Conv2d(dim_model, dim_model, 1),
+        )
+
+        # MHA related flags:
+        self.requires_same_k_q_dimensions = (
+            True  # This mechanism only really supports self attention
+        )
+        self.supports_attention_mask = False
+        self.requires_skip_multi_head = (
+            True  # This mechanism skips the multihead attention altogether
+        )
+        self.requires_squared_context = (
+            True  # Recovering the 2D structure from context assumes squared content
+        )
+
+        self.requires_input_projection = (
+            False  # This mechanism does not require that the MHA projects inputs
+        )
+
+    def forward(self, q: torch.Tensor, *_, **__):
+        # Expose the 2D token structure
+        B, HW, C = q.shape
+        H = int(math.sqrt(HW))
+        assert H * H == HW
+
+        x = q.transpose(-2, -1).reshape(B, C, H, H)
+
+        # Large kernel attention
+        residual = x.clone()
+        x = self.block(x)
+        x = x + residual
+
+        # Get back to B HW C
+        return x.flatten(2, 3).transpose(-2, -1)

xformers/factory/block_factory.py

@@ -278,7 +278,10 @@ def __init__(self, config: xFormerDecoderConfig, **kwargs):
         # Expose attention or feedforward specific capabilities
         self.supports_attention_mask = mha.attention.supports_attention_mask
         self.requires_same_k_q_dimensions = mha.attention.requires_same_k_q_dimensions
-        self.requires_squared_context_length = feedforward.requires_squared_context
+        self.requires_squared_context_length = (
+            feedforward.requires_squared_context
+            or mha.attention.requires_squared_context
+        )
 
         self.causal_attention = (
             mha.attention.causal if hasattr(mha.attention, "causal") else False