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Subdivision Modifier unusal RAM usage
Needs Triage, NormalPublic

Description

System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 441.28

Blender Version
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-12-04 11:32, hash: rBf1aa4d18d49d
Worked: (optional)

Short description of error
Opening the attached examplefile (~60MB) with visible subdivision modifiers the used system RAM is very high (~33GB).
After rendering the used system RAM is "cleared" and the example file only uses about 800MB.
->~31GB unnecessarily used RAM before hitting render.

Exact steps for others to reproduce the error


Opening the attached examplefile "Cookies Subd visible.blend" (~60MB) with visible subdivision modifiers the used system RAM is very high (~33GB).
After rendering the used system RAM is "cleared" and the example file only uses about 800MB.
->~31GB unnecessarily used RAM before hitting render.

File size: 61.804KB
RAM Usage after opening: ~33GB
RAM Usage initializing Render GPU(1x2080ti): ~60GB
RAM Usage while rendering: ~5GB
RAM Usage after render: ~800MB

With hidden subdivion modifier there is a expectable RAM usage (File: "Cookies Subd hidden.blend"):

File size: 61.804KB
RAM Usage after opening: ~360MB
RAM Usage initializing Render GPU(1x2080ti): ~35GB
RAM Usage while rendering: ~5GB
RAM Usage after render: ~400MB

Event Timeline

I can't open the file on my system with 16GB of RAM.

I believe the file has very heavy settings to handle the Subdivision modifier.
If so, this is not considered a bug. The user has to be aware of the limitations when setting up a modifier.

@Sergey Sharybin (sergey), if I'm not mistaken, you've worked with this modifier a few times, any idea why the memory decreases after rendering?