Operating system: Windows 10
Graphics card: NVIDIA GeForce GTX 1080
Broken: 2.80 beta (2018-11-29 15:57, 26d5a3625ed, blender2.8)
Worked: 2.79 (5bd8ac9)
Short description of error
When using duplicate linked objects, the total amount of memory used to render an image in Cycles is the same as if the linked meshes were single-user copies.
Exact steps for others to reproduce the error
Load the default start-up file.
Set the render engine to Cycles.
Delete the default cube.
Add in a suitably vertex-dense object, such as an icosphere subdivision 6.
Render the file and take note of the memory statistic in the image viewer.
"Duplicate linked" (alt-d) the icosphere 2 or 3 times.
Re-render the file and note that the memory used has increased substantially.
Make each icosphere a single-user copy
Re-render the file and note that the memory used is the same as it was in the second render.