# e820 regions and e820 limitation

## DaggyStyle

Greetings,

I want to run a test on my machine to check something, here is my e820:

```
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009ffff] usable

[    0.000000] BIOS-e820: [mem 0x00000000000a0000-0x00000000000fffff] reserved

[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000009e01fff] usable

[    0.000000] BIOS-e820: [mem 0x0000000009e02000-0x0000000009ffffff] reserved

[    0.000000] BIOS-e820: [mem 0x000000000a000000-0x000000000a1fffff] usable

[    0.000000] BIOS-e820: [mem 0x000000000a200000-0x000000000a20afff] ACPI NVS

[    0.000000] BIOS-e820: [mem 0x000000000a20b000-0x000000000affffff] usable

[    0.000000] BIOS-e820: [mem 0x000000000b000000-0x000000000b01ffff] reserved

[    0.000000] BIOS-e820: [mem 0x000000000b020000-0x00000000db4f9fff] usable

[    0.000000] BIOS-e820: [mem 0x00000000db4fa000-0x00000000db693fff] reserved

[    0.000000] BIOS-e820: [mem 0x00000000db694000-0x00000000db823fff] usable

[    0.000000] BIOS-e820: [mem 0x00000000db824000-0x00000000dbc71fff] ACPI NVS

[    0.000000] BIOS-e820: [mem 0x00000000dbc72000-0x00000000dcabffff] reserved

[    0.000000] BIOS-e820: [mem 0x00000000dcac0000-0x00000000dcb50fff] type 20

[    0.000000] BIOS-e820: [mem 0x00000000dcb51000-0x00000000deffffff] usable

[    0.000000] BIOS-e820: [mem 0x00000000df000000-0x00000000dfffffff] reserved

[    0.000000] BIOS-e820: [mem 0x00000000f8000000-0x00000000fbffffff] reserved

[    0.000000] BIOS-e820: [mem 0x00000000fd000000-0x00000000ffffffff] reserved

[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000081f37ffff] usable
```

I want to change the e820 to be this (changes marked with <==):

```
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009ffff] usable

[    0.000000] BIOS-e820: [mem 0x00000000000a0000-0x00000000000fffff] reserved

[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x0000000009e01fff] usable

[    0.000000] BIOS-e820: [mem 0x0000000009e02000-0x0000000009ffffff] reserved

[    0.000000] BIOS-e820: [mem 0x000000000a000000-0x000000000a1fffff] usable

[    0.000000] BIOS-e820: [mem 0x000000000a200000-0x000000000a20afff] ACPI NVS

[    0.000000] BIOS-e820: [mem 0x000000000a20b000-0x000000000affffff] usable

[    0.000000] BIOS-e820: [mem 0x000000000b000000-0x000000000b01ffff] reserved

[    0.000000] BIOS-e820: [mem 0x000000000b020000-0x000000002affffff] usable <==

[    0.000000] BIOS-e820: [mem 0x000000002b000000-0x00000000db693fff] reserved <==

[    0.000000] BIOS-e820: [mem 0x00000000db694000-0x00000000db823fff] usable

[    0.000000] BIOS-e820: [mem 0x00000000db824000-0x00000000dbc71fff] ACPI NVS

[    0.000000] BIOS-e820: [mem 0x00000000dbc72000-0x00000000dcabffff] reserved

[    0.000000] BIOS-e820: [mem 0x00000000dcac0000-0x00000000dcb50fff] type 20

[    0.000000] BIOS-e820: [mem 0x00000000dcb51000-0x00000000deffffff] usable

[    0.000000] BIOS-e820: [mem 0x00000000df000000-0x00000000dfffffff] reserved

[    0.000000] BIOS-e820: [mem 0x00000000f8000000-0x00000000fbffffff] reserved

[    0.000000] BIOS-e820: [mem 0x00000000fd000000-0x00000000ffffffff] reserved

[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x00000003ec18f800] usable <==
```

looking at https://www.kernel.org/doc/html/v4.14/admin-guide/kernel-parameters.html it looks like I should use this kernel params: mem=16451134k memmap=0x2c13e7$0x2b000000

but when I try it, I don't see such changes in the dmesg.

am I doing it correctly?

Thanks,

Dagg.

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