ollamarunner: Memory usage reporting

This provides granular information about the backend memory allocations
required by the runner:
 - Per backend
 - Per layer
 - Weights, cache and graph
 - Allocation status

This can be used for debugging and validating memory estimates.

ml/backend.go

@@ -15,6 +15,10 @@ import (
 
 type Backend interface {
 	Load(ctx context.Context, progress func(float32)) error
+
+	// BackendMemory returns the memory allocations that were made for this model
+	BackendMemory() BackendMemory
+
 	Config() fs.Config
 	Get(name string) Tensor
 	NewContext() Context
@@ -68,6 +72,84 @@ type BackendParams struct {
 	FlashAttention bool
 }
 
+// ErrNoMem is returned when panicing due to insufficient memory. It includes
+// the attempted memory allocation.
+type ErrNoMem struct {
+	BackendMemory
+}
+
+func (e ErrNoMem) Error() string {
+	return fmt.Sprintf("insufficient memory - required allocations: %+v", e.BackendMemory)
+}
+
+type AllocationStatus int
+
+const (
+	// Unallocated memory - have not yet attempted to allocate
+	Unallocated AllocationStatus = iota
+
+	// Failed memory - tried to allocate the memory and did not succeed
+	Failed
+
+	// Allocated memory = tried and succeeded to allocate memory
+	Allocated
+)
+
+// Memory is the size of an allocation and whether it was successful.
+type Memory struct {
+	Size   uint64
+	Status AllocationStatus
+}
+
+func (m Memory) String() string {
+	s := fmt.Sprint(m.Size)
+
+	switch m.Status {
+	case Unallocated:
+		s += "U"
+	case Failed:
+		s += "F"
+	case Allocated:
+		s += "A"
+	}
+
+	return s
+}
+
+// DeviceMemory provides a breakdown of the memory needed
+// per device, such as a CPU or GPU.
+type DeviceMemory struct {
+	// Name is the name of the device as labeled by the backend. It
+	// may not be persistent across instances of the runner.
+	Name string
+
+	// Weights is the per-layer memory needed for the model weights.
+	Weights []Memory
+
+	// Cache is the per-layer memory needed for the KV cache.
+	Cache []Memory
+
+	// Graph is the size of the compute graph. It is not per-layer.
+	Graph Memory
+}
+
+// BackendMemory provides the amount of memory required to load the model
+// per device based on the BackendParams. In some cases, not all required
+// allocations will be known at this point. However, the size of the most recent
+// allocation is guaranteed to be provided so that if it failed, the caller can
+// accommodate that to make forward progress.
+type BackendMemory struct {
+	// InputsWeights are always located on the CPU and cannot be moved
+	InputWeights Memory
+
+	// CPU model components are located in system memory. This does not
+	// include unified memory allocated through the GPU.
+	CPU DeviceMemory
+
+	// GPU model components are located on one or more GPUs.
+	GPUs []DeviceMemory
+}
+
 var backends = make(map[string]func(string, BackendParams) (Backend, error))
 
 func RegisterBackend(name string, f func(string, BackendParams) (Backend, error)) {
@@ -102,7 +184,7 @@ type Context interface {
 	// graph, simply preallocates memory. Typically called with a
 	// worst case graph to ensure all resources are available for
 	// for future inference.
-	Reserve() error
+	Reserve()
 
 	MaxGraphNodes() int
 	Close()