perf: optimize local_block_table memory allocation (#6273)

python/sglang/srt/layers/attention/flashattention_backend.py

@@ -1165,7 +1165,6 @@ class FlashAttentionBackend(AttentionBackend):
             max_virtual_batches = max_bs * (
                 (max_seq_len + attn_chunk_size - 1) // attn_chunk_size
             )
-            max_blocks_per_seq = (max_seq_len + attn_chunk_size - 1) // attn_chunk_size
             max_pages_per_block = (attn_chunk_size + page_size - 1) // page_size
 
             self.decode_cuda_graph_local_attn_metadata = {
@@ -1177,7 +1176,7 @@ class FlashAttentionBackend(AttentionBackend):
                 ),
                 "local_block_table": torch.zeros(
                     max_virtual_batches,
-                    max_blocks_per_seq * max_pages_per_block,
+                    max_pages_per_block,
                     dtype=torch.int32,
                     device=self.device,
                 ),