llm: Estimate projector memory correctly for Ollama engine

The Llama engine always places vision projectors on the first GPU
if one exists. However, the Ollama engine groups it with the output
layer, which means the projector is only offloaded if all other layers
are offloaded. The memory estimation code always assumes the former
layout - this changes it to use the correct layout based on the engine.

This addresses two impacts of the current behavior:
 - In multi-GPU setups, we can crash with OOM errors when we try to
   allocate memory on a full GPU while another still has space.
 - If the vision projector is large, it may prevent us from offloading
   anything when we could have fit some of the text layers.

llm/memory.go

@@ -85,8 +85,12 @@ func EstimateGPULayers(gpus []discover.GpuInfo, f *ggml.GGML, projectors []strin
 	var graphOffload uint64
 
 	// Projectors loaded into GPU0 only
-	var projectorWeights uint64
-	var projectorGraph uint64
+	var llamaEngineProjectorWeights uint64
+	var llamaEngineProjectorGraph uint64
+
+	// Projectors loaded with output layer
+	var ollamaEngineProjectorWeights uint64
+	var ollamaEngineProjectorGraph uint64
 
 	// Conditional output size on GPU 0
 	var memoryLayerOutput uint64
@@ -112,14 +116,15 @@ func EstimateGPULayers(gpus []discover.GpuInfo, f *ggml.GGML, projectors []strin
 
 	for _, projector := range projectors {
 		weight, graph := projectorMemoryRequirements(projector)
-		projectorWeights += weight
-		projectorGraph += graph
+		llamaEngineProjectorWeights += weight
+		llamaEngineProjectorGraph += graph
 
 		// multimodal models require at least 2048 context
 		opts.NumCtx = max(opts.NumCtx, 2048)
 	}
-	if projectorWeights == 0 && projectorGraph == 0 {
-		projectorWeights, projectorGraph = f.VisionGraphSize()
+	if llamaEngineProjectorWeights == 0 && llamaEngineProjectorGraph == 0 {
+		ollamaEngineProjectorWeights, ollamaEngineProjectorGraph = f.VisionGraphSize()
+		opts.NumCtx = max(opts.NumCtx, 2048)
 	}
 
 	layers := f.Tensors().GroupLayers()
@@ -164,6 +169,7 @@ func EstimateGPULayers(gpus []discover.GpuInfo, f *ggml.GGML, projectors []strin
 		graphFullOffload = graphPartialOffload
 	}
 
+	// Output layer handled at the end if we have space
 	if layer, ok := layers["output_norm"]; ok {
 		memoryLayerOutput += layer.Size()
 	}
@@ -173,8 +179,7 @@ func EstimateGPULayers(gpus []discover.GpuInfo, f *ggml.GGML, projectors []strin
 		memoryLayerOutput += layer.Size()
 	}
 
-	// Output layer handled at the end if we have space
-	gpuZeroOverhead := projectorWeights + projectorGraph
+	gpuZeroOverhead := llamaEngineProjectorWeights + llamaEngineProjectorGraph
 
 	// Reduce set of GPUs to only those that have sufficient space to fit overhead and at least one layer
 	var layerCount int
@@ -217,6 +222,8 @@ func EstimateGPULayers(gpus []discover.GpuInfo, f *ggml.GGML, projectors []strin
 	if len(gpusWithSpace) > 0 {
 		gpuZeroID = gpusWithSpace[0].i
 		gpuAllocations[gpuZeroID] += gpuZeroOverhead
+	} else {
+		overflow += gpuZeroOverhead
 	}
 
 	// For all the layers, find where they can fit on the GPU(s)
@@ -257,21 +264,24 @@ func EstimateGPULayers(gpus []discover.GpuInfo, f *ggml.GGML, projectors []strin
 	}
 
 	// Determine if we need to consider output then find where it fits
-	if memoryLayerOutput > 0 && (opts.NumGPU < 0 || layerCount < opts.NumGPU) {
-		for j := len(gpusWithSpace); j > 0; j-- {
-			g := gpusWithSpace[layerCount%j]
-			used := gpuAllocations[g.i] + max(graphPartialOffload, graphFullOffload)
-			if g.g.FreeMemory > overhead+used+memoryLayerOutput {
-				gpuAllocations[g.i] += memoryLayerOutput
-				layerCounts[g.i]++
-				layerCount++
-				break
+	memoryLastLayer := memoryLayerOutput + ollamaEngineProjectorWeights + ollamaEngineProjectorGraph
+	if memoryLastLayer > 0 {
+		if opts.NumGPU < 0 || layerCount < opts.NumGPU {
+			for j := len(gpusWithSpace); j > 0; j-- {
+				g := gpusWithSpace[layerCount%j]
+				used := gpuAllocations[g.i] + max(graphPartialOffload, graphFullOffload)
+				if g.g.FreeMemory > overhead+used+memoryLastLayer {
+					gpuAllocations[g.i] += memoryLastLayer
+					layerCounts[g.i]++
+					layerCount++
+					break
+				}
 			}
 		}
 
 		if layerCount < int(f.KV().BlockCount())+1 {
 			fullyLoaded = false
-			overflow += memoryLayerOutput
+			overflow += memoryLastLayer
 		}
 	}
 
@@ -329,8 +339,8 @@ func EstimateGPULayers(gpus []discover.GpuInfo, f *ggml.GGML, projectors []strin
 		memoryLayerOutput:   memoryLayerOutput,
 		graphFullOffload:    graphFullOffload,
 		graphPartialOffload: graphPartialOffload,
-		projectorWeights:    projectorWeights,
-		projectorGraph:      projectorGraph,
+		projectorWeights:    llamaEngineProjectorWeights + ollamaEngineProjectorWeights,
+		projectorGraph:      llamaEngineProjectorGraph + ollamaEngineProjectorGraph,
 	}
 
 	if gpus[0].Library == "cpu" {