Now I have the same problem.
I know 4 GB Ram is not much, but it always was enough for BF4 or any other games.
But now my RAM goes up to 98% or more when I play BF4 and the game starts stuttering till it becomes unplayable.
When I quit BF4 (via the menu) RAM usage still stays this high.
I checked the task manager for a running bf4.exe etc. but the game always was shut down correctly. However, the ram usuage stays this high until I reboot. Any other games don't cause this problem.
Operating System
Windows 8.1 64-bit
CPU
Intel Core i5 750 @ 2.67GHz 48 °C
Lynnfield 45nm Technology
RAM
4,00GB Dual-Channel DDR3 @ 799MHz (9-9-9-24)
Motherboard
ASRock P55 Pro (CPUSocket) 33 °C
Graphics
W2361 (1920x1080@60Hz)
1024MB ATI AMD Radeon HD 5700 Series (Sapphire/PCPartner) 40 °C
Storage
111GB Crucial_CT120M500SSD1 ATA Device (SSD)
1863GB Seagate ST2000DM001-1CH164 ATA Device (SATA) 37 °C
931GB Hitachi HDS721010CLA332 USB Device (USB (SATA)) 38 °C
Optical Drives
HL-DT-ST DVDRAM GH24NSB0 ATA Device
Audio
Logitech G930 Headset