set kms specific resolution at boot time

i'm trying to set a specific resolution for kms, at boot time. by default kms choose the highest resolution available (2500x1600) which is a bit hard to read. i'd like to set 1440x900 instead. i tried two things via grub, the first one:

GRUB_GFXMODE=1440x900
GRUB_GFXPAYLOAD_LINUX=keep
GRUB_GFXPAYLOAD_LINUX=1440x900

but that didn't help, the system act just the same, no matter if it is there or not, it just continue to use 2500x1600. the other thing i tried instead is setting a kernel parameter like so:

GRUB_CMDLINE_LINUX_DEFAULT="video=1440x900"

that kind of helped a bit, the resolution changed, it's much better and readable but then, the virtual_size didn't change accordingly, it's still 2500x1600, meaning my tty is much bigger than the screen itself and so i only see the upper_left part of a larger term. how can i force kms to a specific resolution ? thanks