ml: Enable support for flash attention

The GGML flash attention kernel has specific requirements for
padding and permutation. This adds support to the KV cache
for conforming to these requirements so that flash attention
can be enabled.

Flash attention can be used in the same situations as the llama
engine and is enabled by the user in the same way.

runner/ollamarunner/runner.go

@@ -818,7 +818,7 @@ func Execute(args []string) error {
 	batchSize := fs.Int("batch-size", 512, "Batch size")
 	numGPULayers := fs.Int("n-gpu-layers", 0, "Number of layers to offload to GPU")
 	mainGPU := fs.Int("main-gpu", 0, "Main GPU")
-	_ = fs.Bool("flash-attn", false, "Enable flash attention")
+	flashAttention := fs.Bool("flash-attn", false, "Enable flash attention")
 	kvSize := fs.Int("ctx-size", 2048, "Context (or KV cache) size")
 	kvCacheType := fs.String("kv-cache-type", "", "quantization type for KV cache (default: f16)")
 	port := fs.Int("port", 8080, "Port to expose the server on")
@@ -863,7 +863,6 @@ func Execute(args []string) error {
 	}
 
 	// TODO(jessegross): Parameters that need to be implemented:
-	//	flash-attn
 	//	no-mmap
 	//	mlock
 
@@ -878,10 +877,11 @@ func Execute(args []string) error {
 	}
 
 	params := ml.BackendParams{
-		NumThreads:   *threads,
-		NumGPULayers: *numGPULayers,
-		MainGPU:      *mainGPU,
-		TensorSplit:  tensorSplitFloats,
+		NumThreads:     *threads,
+		NumGPULayers:   *numGPULayers,
+		MainGPU:        *mainGPU,
+		TensorSplit:    tensorSplitFloats,
+		FlashAttention: *flashAttention,
 	}
 
 	server.ready.Add(1)