You already found lsmem:

$ lsmem

Then, lspci will give the information about the graphic card's memory and mappings. First list the PCI bus:

$ lscpi

Identify your card (the numbers on the left). Let's say that it is listed as 00:02.0.

$ lspci -v -s 00:02.0

You already found lsmem:

$ lsmem

Then, lspci will give the information about the graphic card's memory and mappings. First list the PCI bus:

$ lscpi

Identify your card (the numbers on the left). Let's say that it is listed as 00:02.0.

$ lspci -v -s 00:02.0

For the full video memory, that doesn't have to be mapped, you can do:

$ glxinfo | egrep -i 'device|memory'