Thank you Glenn !
Your answer was very helpful, the Cutmem i think worked, but the other one did not.
From a machine that had already usuntu installed and running, i knew that if the modifications worked, then if i run in terminal sudo Dmesg , i should see something like this:
[ 0.000000] reserve setup_data: [mem 0x00000000b4018000-0x00000000b401cfff] reserved
[ 0.000000] reserve setup_data: [mem 0x00000000b2018000-0x00000000b201cfff] reserved
1) So, I started from scratch with an ubuntu iso and rufus. and modified boot/grub/grug.cfg like you said.
menuentry "Ubuntu (safe graphics)" {
set gfxpayload=keep
linux /casper/vmlinuz nomodeset file=/cdrom/preseed/ubuntu.seed maybe-ubiquity quiet splash ---
memmap=16K\$0x0000000B4018000,16K\$0x0000000B2018000,4K\$0x0000000B401C000,4K\$0x0000000B201C000
initrd /casper/initrd
}
I was able to boot ubuntu from liveusb, and did sudo Dmesg, i could not find any address for b4018000 nor b2018000
so pretty much for me it means it failed, and if i run any program later on there is a high chance that it will crash because of bad memory.
2) So i went back to boot/grub/grug.cfg and added as the first lines the one you told me:
cutmem 2949216K 2949232K
cutmem 2916448K 2916464K
cutmem 2949232K 2949236K
cutmem 2916464K 2916468K
booted ubuntu live usb, did sudo dmesg ,and i found some "unusable" addresses for bios-e820 that matched b4018000 and b2018000
[ 0.000000] BIOS-e820: [mem 0x00000000b2018000-0x00000000b201cfff] unusable
[ 0.000000] BIOS-e820: [mem 0x00000000b4018000-0x00000000b401cfff] unusable
so pretty much i think the cutmem worked! just need to test for many hours that there are no crashes using live usb.
At least now i might be able to boot many different linux distros from live USB too! which is what i was looking for!!
thanks!