RADV driver, for reasons unknown to me, reluctant to use GTT memory
By radeontop monitoring I see that GPU additionally to VRAM also has GTT I suppose this is part of main RAM of computer.
RADV driver, for reasons unknown to me, reluctant to use GTT memory for its needs. And if by the time the game was launched, VRAM was filled. Then the game will has serious FPS issues. Problems are actually in all absolutely games, it's just that some games need more memory, others less. AMDVLK, on the other hand, uses GTT memory very well and manages to run without FPS drops even if the VRAM was full before launching the game.
Hitting 16GB VRAM is very easy if you use a 4K monitor and use a couple of browsers with each one opening 10 windows (not tabs) with sites.
One of the game which highly sensitive to lack of memory is "The Dark Pictures Anthology: House of Ashes".
You can see that the FPS sags less than 10 frames if you fill in VRAM by 10GB before launch, leaving the game with only 6GB of free video memory.
Demonstration: https://www.youtube.com/watch?v=YlVUbVdmtSI
CPU: Ryzen 3950X
GPU: Radeon 6900XT
RAM: 64Gb