test out flash attention in GPT

Author: lucidrains

memory_efficient_attention_pytorch/transformer.py

@@ -3,7 +3,7 @@
 import torch.nn.functional as F
 
 from einops import rearrange
-from memory_efficient_attention_pytorch import Attention
+from memory_efficient_attention_pytorch import FlashAttention, Attention
 from memory_efficient_attention_pytorch.reversible import ReversibleSequence
 
 def exists(val):
@@ -51,6 +51,7 @@ def __init__(
         heads = 8,
         ff_mult = 4,
         ff_chunks = 1,
+        use_flash_attn = True,
         **kwargs
     ):
         super().__init__()
@@ -59,10 +60,12 @@ def __init__(
         self.token_emb = nn.Embedding(num_tokens, dim)
         self.pos_emb = nn.Embedding(max_seq_len, dim)
 
+        attn_klass = FlashAttention if use_flash_attn else partial(Attention, memory_efficient = True)
+
         self.layers = nn.ModuleList([])
         for _ in range(depth):
             self.layers.append(nn.ModuleList([
-                PreNorm(dim, Attention(dim = dim, dim_head = dim_head, heads = heads, causal = causal, **kwargs)),
+                PreNorm(dim, attn_klass(dim = dim, dim_head = dim_head, heads = heads, causal = causal, **kwargs)),
                 PreNorm(dim, FeedForward(dim = dim, mult = ff_mult, chunks = ff_chunks)),
             ]))
 

setup.py

@@ -3,7 +3,7 @@
 setup(
   name = 'memory-efficient-attention-pytorch',
   packages = find_packages(exclude=[]),
-  version = '0.0.23',
+  version = '0.0.25',
   license='MIT',
   description = 'Memory Efficient Attention - Pytorch',
   long_description_content_type = 'text/markdown',

tests/test.py

@@ -91,7 +91,9 @@ def test_flash_attn_gradients_equal():
     k = torch.randn(1, 8, 1024, 512).requires_grad_()
     v = torch.randn(1, 8, 1024, 512).requires_grad_()
 
-    o = attention(q, k, v, causal = False)
+    mask = torch.ones(1, 1024).bool()
+
+    o = attention(q, k, v, mask = mask, causal = True)
     o.sum().backward()
 
     dq_grad = q.grad.clone()
@@ -102,7 +104,7 @@ def test_flash_attn_gradients_equal():
     k.grad.zero_()
     v.grad.zero_()
 
-    flash_o = FlashAttentionFunction.apply(q, k, v, None, False, 64, 64)
+    flash_o = FlashAttentionFunction.apply(q, k, v, mask, True, 64, 64)
     flash_o.sum().backward()
 
     flash_dq_grad = q.grad.clone()

train.py

@@ -18,7 +18,7 @@
 LEARNING_RATE = 2e-4
 VALIDATE_EVERY  = 100
 GENERATE_EVERY  = 500
-GENERATE_LENGTH = 4096
+GENERATE_LENGTH = 1024
 SEQ_LEN = 4096
 
 # helpers
@@ -43,10 +43,10 @@ def decode_tokens(tokens):
     depth = 6,
     heads = 8,
     causal = True,
-    memory_efficient = True,
     q_bucket_size = 256,
     k_bucket_size = 256,
-    ff_chunks = 5
+    ff_chunks = 5,
+    use_flash_attn = True
 )
 
 model = AutoregressiveWrapper(model)