How to pass memmap parameters to kernel via grub to not use bad ram

memmap linux kernel parameters are:

        mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
                        Amount of memory to be used when the kernel is not able
                        to see the whole system memory or for test.
                        [IA-32] Use together with memmap= to avoid physical
                        address space collisions. Without memmap= PCI devices
                        could be placed at addresses belonging to unused RAM.

        mem=nopentium   [BUGS=IA-32] Disable usage of 4MB pages for kernel
                        memory.

        memmap=exactmap [KNL,IA-32] Enable setting of an exact
                        E820 memory map, as specified by the user.
                        Such memmap=exactmap lines can be constructed based on
                        BIOS output or other requirements. See the memmap=nn@ss
                        option description.

        memmap=nn[KMG]@ss[KMG]
                        [KNL] Force usage of a specific region of memory
                        Region of memory to be used, from ss to ss+nn.

        memmap=nn[KMG]#ss[KMG]
                        [KNL,ACPI] Mark specific memory as ACPI data.
                        Region of memory to be used, from ss to ss+nn.

        memmap=nn[KMG]$ss[KMG]
                        [KNL,ACPI] Mark specific memory as reserved.
                        Region of memory to be used, from ss to ss+nn.

When passing via grub you need to escape the $:

ie: memmap 128M\$1024M 

Without the escaping, memmap doesn't behave correctly.

In /etc/default/grub you need to escape \ too.

So option as to be writed this way: memmap 128M\\\$512M

Several memmap options could be used as the same time.