Comment 34 for bug 1737423

Looks like the RAM size is correctly detected:
[ 10.572891] nouveau [ DEVICE][0000:03:09.0] BOOT0 : 0x04a100a1
[ 10.572897] nouveau [ DEVICE][0000:03:09.0] Chipset: NV44A (NV4A)
[ 10.572903] nouveau [ DEVICE][0000:03:09.0] Family : NV40
[ 10.579195] nouveau [ VBIOS][0000:03:09.0] checking PRAMIN for image...
[ 10.579208] nouveau [ VBIOS][0000:03:09.0] ... signature not found
[ 10.579213] nouveau [ VBIOS][0000:03:09.0] checking PROM for image...
[ 10.900540] nouveau [ VBIOS][0000:03:09.0] ... appears to be valid
[ 10.900544] nouveau [ VBIOS][0000:03:09.0] using image from PROM
[ 10.900760] nouveau [ VBIOS][0000:03:09.0] BIT signature found
[ 10.900767] nouveau [ VBIOS][0000:03:09.0] version 05.44.a2.10.01
[ 10.913241] nouveau [ DEVINIT][0000:03:09.0] adaptor not initialised
[ 10.913253] nouveau [ VBIOS][0000:03:09.0] running init tables
[ 10.931444] nouveau [ PFB][0000:03:09.0] RAM type: DDR2
[ 10.931448] nouveau [ PFB][0000:03:09.0] RAM size: 256 MiB

You can use HWE stack for newer kernel and newer Xorg:
https://wiki.ubuntu.com/Kernel/LTSEnablementStack#Ubuntu_14.04_LTS_-_Trusty_Tahr
[ 10.931451] nouveau [ PFB][0000:03:09.0] ZCOMP: 0 tags