I know this has been asked many times before, but I feel I need to bring it up again because I too am affected.
I have an Asus N551ZU laptop. It has a FX-7600P with R7 APU coupled with a R9 M280X dGPU that has 2GB of dedicated memory. The problem is, GTAV is only detecting the APU's R7. I have already set up switchable graphics to High Performance for the game, but it's still only using the R7 (notable because the game claims that the GPU only has 1GB of RAM, which is preallocated). If it's using the dGPU it should claim that I have 2GB of RAM.
Which brings me to the second topic- I thought the Kaveri-class APUs have HSA. I have 16GB of RAM on this laptop (2133MHz ones no less, to max out the potential of the APU). Why is the game only detecting the 1GB Windows preallocated for the GPU and ignoring the other 15GB of RAM? I thought the game should claim that it has as much RAM as that's free on the laptop. Idling, I have 11GB free. So the game should claim at least 6GB? I find it unlikely that the game fills up all my free RAM except those preallocated to the GPU?
The biggest issue of this is, well, the game wouldn't run unless I tell it to ignore the limits or knock things down to DX10 mode. Apparently 1 GB isn't enough for GTA V even at lowest settings in DX11 (everything at normal, all antialiasing disabled). Also, I get terrible draw distances, I get issues where the road suddenly disappears and my car is floating on air and I cannot see where I'm supposed to go. I have to stop the car for the buildings and textures to load. And as you know, in GTA, this is not acceptable- stopping for a second could be the death of you either at the hands of the cops or rival criminals. And I'm sure it's not a disk bottleneck, the laptop has a SSD as it's sole drive.