Allow for lazy loading of npz files, use it in llama to reduce memory usage in the cpu version. (#141)

candle-nn/src/var_builder.rs

@@ -1,4 +1,4 @@
-use candle::{safetensors::SafeTensors, DType, Device, Error, Shape, Tensor};
+use candle::{safetensors::SafeTensors, DType, Device, Error, Result, Shape, Tensor};
 use std::collections::HashMap;
 use std::sync::Arc;
 
@@ -9,6 +9,7 @@ enum Tensors<'a> {
         routing: HashMap<String, usize>,
         safetensors: Vec<SafeTensors<'a>>,
     },
+    Npz(candle::npy::NpzTensors),
     TensorMap(HashMap<String, Tensor>),
     Zeros,
 }
@@ -53,6 +54,15 @@ impl<'a> TensorData<'a> {
             dtype,
         }
     }
+
+    fn from_npz<P: AsRef<std::path::Path>>(file: P, dtype: DType, device: &Device) -> Result<Self> {
+        let npz = candle::npy::NpzTensors::new(file)?;
+        Ok(Self {
+            tensors: Tensors::Npz(npz),
+            device: device.clone(),
+            dtype,
+        })
+    }
 }
 
 #[derive(Clone)]
@@ -88,6 +98,18 @@ impl<'a> VarBuilder<'a> {
         }
     }
 
+    pub fn from_npz<P: AsRef<std::path::Path>>(
+        file: P,
+        dtype: DType,
+        device: &Device,
+    ) -> Result<Self> {
+        let data = TensorData::from_npz(file, dtype, device)?;
+        Ok(Self {
+            data: Arc::new(data),
+            path: vec![],
+        })
+    }
+
     pub fn push_prefix(&self, s: &str) -> Self {
         let mut path = self.path.clone();
         path.push(s.to_string());
@@ -112,7 +134,7 @@ impl<'a> VarBuilder<'a> {
 }
 
 impl<'a> VarBuilder<'a> {
-    pub fn get<S: Into<Shape>>(&self, s: S, tensor_name: &str) -> candle::Result<Tensor> {
+    pub fn get<S: Into<Shape>>(&self, s: S, tensor_name: &str) -> Result<Tensor> {
         let data = self.data.as_ref();
         let s: Shape = s.into();
         let path = if self.path.is_empty() {
@@ -128,6 +150,9 @@ impl<'a> VarBuilder<'a> {
                     path: path.to_string(),
                 })?
                 .clone(),
+            Tensors::Npz(npz) => npz.get(&path)?.ok_or_else(|| Error::CannotFindTensor {
+                path: path.to_string(),
+            })?,
             Tensors::SafeTensorWithRouting {
                 routing,
                 safetensors,