Add a structural loadparams!

NEWS.md

@@ -12,6 +12,7 @@ been removed in favour of MLDatasets.jl.
 * The DataLoader is now compatible with generic dataset types implementing `MLUtils.numobs` and `MLUtils.getobs`.
 * Added [truncated normal initialisation](https://github.com/FluxML/Flux.jl/pull/1877) of weights.
 * The `Flux.Diagonal` layer is now called `Scale`, and accepts an activation function.
+* `loadparams!` is replaced by [`loadmodel!`](https://github.com/FluxML/Flux.jl/pull/1875) which copies trainable + non-trainable parameters and performs more thorough structural checking
 
 ## v0.12.10
 * `Dropout`/`AlphaDropout` now supports [user-specified RNGs](https://github.com/FluxML/Flux.jl/pull/1838)

Project.toml

@@ -29,7 +29,7 @@ Adapt = "3.0"
 ArrayInterface = "3.1, 4, 5"
 CUDA = "3"
 ChainRulesCore = "1.12"
-Functors = "0.2.1"
+Functors = "0.2.8"
 MLUtils = "0.2"
 MacroTools = "0.5"
 NNlib = "0.8.2"

docs/src/saving.md

@@ -2,7 +2,7 @@
 
 You may wish to save models so that they can be loaded and run in a later
 session. The easiest way to do this is via
-[BSON.jl](https://github.com/MikeInnes/BSON.jl).
+[BSON.jl](https://github.com/JuliaIO/BSON.jl).
 
 Save a model:
 
@@ -36,7 +36,6 @@ Chain(
   Dense(5 => 2),                        # 12 parameters
   NNlib.softmax,
 )                   # Total: 4 arrays, 67 parameters, 524 bytes.
-
 ```
 
 Models are just normal Julia structs, so it's fine to use any Julia storage
@@ -46,15 +45,17 @@ versions of Flux).
 
 !!! note
 
-    If a saved model's weights are stored on the GPU, the model will not load
+    If a saved model's parameters are stored on the GPU, the model will not load
     later on if there is no GPU support available. It's best to [move your model
     to the CPU](gpu.md) with `cpu(model)` before saving it.
 
-## Saving Model Weights
+!!! warning
 
-In some cases it may be useful to save only the model parameters themselves, and
-rebuild the model architecture in your code. You can use `params(model)` to get
-model parameters.
+    Previous versions of Flux suggested saving only the model weights using
+    `@save "mymodel.bson" params(model)`.
+    This is no longer recommended and even strongly discouraged.
+    Saving models this way will only store the trainable parameters which
+    will result in incorrect behavior for layers like `BatchNorm`.
 
 ```Julia
 julia> using Flux
@@ -64,28 +65,27 @@ Chain(Dense(10, 5, NNlib.relu), Dense(5, 2), NNlib.softmax)
 
 julia> weights = Flux.params(model);
 
-julia> using BSON: @save
-
-julia> @save "mymodel.bson" weights
-```
-
-You can easily load parameters back into a model with `Flux.loadparams!`.
+Loading the model as shown above will return a new model with the stored parameters.
+But sometimes you already have a model, and you want to load stored parameters into it.
+This can be done as
 
 ```julia
-julia> using Flux
+using Flux: loadmodel!
+using BSON: @load
 
-julia> model = Chain(Dense(10 => 5,relu),Dense(5 => 2),softmax)
-Chain(Dense(10, 5, NNlib.relu), Dense(5, 2), NNlib.softmax)
+# some predefined model
+model = Chain(Dense(10 => 5, relu), Dense(5 => 2), softmax)
 
-julia> using BSON: @load
+# load one model into another
+model = loadmodel!(model, @load("mymodel.bson"))
+```
 
-julia> @load "mymodel.bson" weights
+This ensures that the model loaded from `"mymodel.bson"` matches the structure of `model`. [`Flux.loadmodel!`](@ref) is also convenient for copying parameters between models in memory.
 
-julia> Flux.loadparams!(model, weights)
+```@docs
+Flux.loadmodel!
 ```
 
-The new `model` we created will now be identical to the one we saved parameters for.
-
 ## Checkpointing
 
 In longer training runs it's a good idea to periodically save your model, so that you can resume if training is interrupted (for example, if there's a power cut). You can do this by saving the model in the [callback provided to `train!`](training/training.md).

src/Flux.jl

@@ -46,6 +46,8 @@ include("layers/normalise.jl")
 include("layers/upsample.jl")
 include("layers/show.jl")
 
+include("loading.jl")
+
 include("outputsize.jl")
 
 include("data/Data.jl")

src/deprecations.jl

@@ -48,6 +48,16 @@ function Diagonal(size::Tuple; kw...)
   Scale(size...; kw...)
 end
 
+# Deprecate this eventually once saving models w/o structure is no more
+function loadparams!(m, xs)
+  Base.depwarn("loadparams! will be deprecated eventually. Use loadmodel! instead.", :loadparams!)
+  for (p, x) in zip(params(m), xs)
+    size(p) == size(x) ||
+      error("Expected param size $(size(p)), got $(size(x))")
+    copyto!(p, x)
+  end
+end
+
 # Channel notation: Changed to match Conv, but very softly deprecated!
 # Perhaps change to @deprecate for v0.14, but there is no plan to remove these.
 Dense(in::Integer, out::Integer, σ = identity; kw...) =

src/functor.jl

@@ -85,14 +85,6 @@ function params(m...)
   return ps
 end
 
-function loadparams!(m, xs)
-  for (p, x) in zip(params(m), xs)
-    size(p) == size(x) ||
-      error("Expected param size $(size(p)), got $(size(x))")
-    copyto!(p, x)
-  end
-end
-
 struct FluxCUDAAdaptor end
 adapt_storage(to::FluxCUDAAdaptor, x) = CUDA.cu(x)
 adapt_storage(to::FluxCUDAAdaptor, x::Zygote.FillArrays.AbstractFill) = CUDA.cu(collect(x))

src/loading.jl

@@ -0,0 +1,99 @@
+loadleaf!(dst, src, err) = dst
+loadleaf!(dst::AbstractArray, src, err) =
+  error("Tried to copy $src into an array destination; this is not allowed.")
+loadleaf!(dst, src::AbstractArray, err) =
+  error("Tried to copy an array to $dst; this is not allowed.")
+function loadleaf!(dst::AbstractArray, src::Bool, err)
+  if iszero(src)
+    dst .= src
+  else
+    error("Cannot copy boolean parameter == true to non-zero parameter.")
+  end
+  return dst
+end
+loadleaf!(dst::Bool, src::AbstractArray, err) = iszero(dst) ? dst :
+  error("Cannot copy non-zero parameter to boolean parameter == true.")
+function loadleaf!(dst::AbstractArray, src::AbstractArray, err)
+  (size(dst) == size(src)) || throw(err)
+  copyto!(dst, src)
+end
+
+_tie_check(dst::Bool, src::AbstractArray) = iszero(dst) ||
+  error("Encountered tied parameter with boolean source at some nodes and non-boolean sources at others.")
+_tie_check(dst::AbstractArray, src::Bool) = (iszero(dst) && iszero(src)) ||
+  error("Encountered tied parameter with boolean source at some nodes and non-boolean sources at others.")
+_tie_check(dst::AbstractArray, src::AbstractArray) = (dst == src) ||
+  error("Encountered tied destination parameters with untied and mismatched sources.")
+_tie_check(dst, src) = true
+
+_bool_tie_check(dst, src) = true
+
+"""
+    loadmodel!(dst, src)
+
+Copy all the parameters (trainable and non-trainable) from `src` into `dst`.
+
+Recursively walks `dst` and `src` together using [`Functors.children`](@ref),
+and calling `copyto!` on parameter arrays or throwing an error when there is a mismatch.
+Non-array elements (such as activation functions) are not copied and need not match.
+Zero bias vectors and `bias=false` are considered equivalent
+(see extended help for more details).
+
+# Examples
+```julia
+julia> dst = Chain(Dense(Flux.ones32(2, 5, tanh)), Dense(2 => 1; bias = [1f0]))
+Chain(
+  Dense(5 => 2, tanh),                  # 12 parameters
+  Dense(2 => 1),                        # 3 parameters
+)                   # Total: 4 arrays, 15 parameters, 316 bytes.
+
+julia> dst[1].weight ≈ ones(2, 5)  # by construction
+true
+
+julia> src = Chain(Dense(5 => 2, relu), Dense(2 => 1, bias=false));
+
+julia> Flux.loadmodel!(dst, src);
+
+julia> dst[1].weight ≈ ones(2, 5)  # values changed
+false
+
+julia> iszero(dst[2].bias)
+true
+```
+
+# Extended help
+
+Throws an error when:
+- `dst` and `src` do not share the same fields (at any level)
+- the sizes of leaf nodes are mismatched between `dst` and `src`
+- copying non-array values to/from an array parameter
+  (except inactive parameters described below)
+- `dst` is a "tied" parameter (i.e. refers to another parameter) and
+  loaded into multiple times with mismatched source values
+
+Inactive parameters can be encoded by using the boolean value `false` instead of an array.
+If `dst == false` and `src` is an all-zero array, no error will be raised (and no values copied);
+however, attempting to copy a non-zero array to an inactive parameter will throw an error.
+Likewise, copying a `src` value of `false` to any `dst` array is valid,
+but copying a `src` value of `true` will error.
+"""
+function loadmodel!(dst, src; cache = Base.IdSet())
+  ldsts, _ = functor(dst)
+  lsrcs, _ = functor(src)
+  (keys(ldsts) == keys(lsrcs)) ||
+    throw(ArgumentError("Tried to load $src into $dst but the structures do not match."))
+
+  err = DimensionMismatch("Tried to load $src into $dst but the parameter sizes do not match.")
+  foreach(ldsts, lsrcs) do ldst, lsrc
+    if ldst in cache # we already loaded this parameter before
+      _tie_check(ldst, lsrc) && return ldst
+    elseif Functors.isleaf(ldst) # our first time loading this leaf
+      push!(cache, ldst)
+      loadleaf!(ldst, lsrc, err)
+    else # this isn't a leaf
+      loadmodel!(ldst, lsrc; cache = cache)
+    end
+  end
+
+  return dst
+end