Lfs::FileTranformer caches .gitattributes parser

Prevents `.gitattributes` blob lookup being repeated for every file checked at a given ref

app/services/lfs/file_transformer.rb

@@ -36,7 +36,11 @@ module Lfs
     private
 
     def lfs_file?(file_path)
-      repository.attributes_at(branch_name, file_path)['filter'] == 'lfs'
+      cached_attributes.attributes(file_path)['filter'] == 'lfs'
+    end
+
+    def cached_attributes
+      @cached_attributes ||= Gitlab::Git::AttributesAtRefParser.new(repository, branch_name)
     end
 
     def create_lfs_object!(lfs_pointer_file, file_content)

lib/gitlab/git/repository.rb

@@ -1002,8 +1002,9 @@ module Gitlab
       # This only checks the root .gitattributes file,
       # it does not traverse subfolders to find additional .gitattributes files
       #
-      # This method is around 30 times slower than `attributes`,
-      # which uses `$GIT_DIR/info/attributes`
+      # This method is around 30 times slower than `attributes`, which uses
+      # `$GIT_DIR/info/attributes`. Consider caching AttributesAtRefParser
+      # and reusing that for multiple calls instead of this method.
       def attributes_at(ref, file_path)
         parser = AttributesAtRefParser.new(self, ref)
         parser.attributes(file_path)