Hi Guys:

My machine has 8G memory, when I use kernel boot parameter mem=5G , it only display ¡°4084 M¡± using ¡°free ¨Cm ¡°. 
where the ¡°5120-4084 = 1036M ¡° memory run?

# /bin/uname -a
Linux dom0-93 3.0.13-0.27-default #1 SMP Wed Feb 15 13:33:49 UTC 2012 (d73692b) x86_64 x86_64 x86_64 GNU/Linux

dom0-93:~ # free -m
total used free shared buffers cached
Mem: 4084 259 3824 0 6 84
-/+ buffers/cache: 169 3915
Swap: 1916 0 1916
dom0-93:~ # cat /proc/cmdline 
root=/dev/disk/by-id/cciss-3600508b100104839535656314933001b-part1 resume=/dev/disk/by-id/cciss-3600508b100104839535656314933001b-part2 splash=silent crashkernel=256M-:128M vga=0x317 mem=5120M


when I didn't append "mem=" parmeter, "free -m " shows that total memory is  7892M ,
it only eat up  300M (8192-7892), though I don't know where the 300M memory go.

why?