Re: [PATCH 2/2] arm64: add support for 43bit physical address

From: Nikunj Kela (nkela)
Date: Tue Jul 03 2018 - 14:35:40 EST

We are trying to reduce the memory allocation needed for kdump kernel. We want to reserve less than 32M for kdump kernel if possible. We are able to get ~14M saving by the proposed change. Below are the numbers before and after the proposed change:

With 48 bit physical address and 30 bit section size:

Memory: 23052K/49152K available (3460K kernel code, 296K rwdata, 2436K rodata, 204K init, 179K bss, 26100K reserved, 0K cma-reserved)

With 43 bit physical address and 27bit section size:

Memory: 37284K/49152K available (3596K kernel code, 296K rwdata, 2408K rodata, 208K init, 173K bss, 11868K reserved, 0K cma-reserved)

From: Catalin Marinas <catalin.marinas@xxxxxxx>
Sent: Tuesday, July 3, 2018 7:56 AM
To: Nikunj Kela (nkela)
Cc: Will Deacon; xe-kernel@xxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [PATCH 2/2] arm64: add support for 43bit physical address

On Mon, Jul 02, 2018 at 02:04:51PM -0700, Nikunj Kela wrote:
> This patch adds support for 43bit physical address. Additionally,
> this patch adds support for 27bit section size. This is useful in
> reducing kernel memory usage. One usecase is in kdump kernel.

Some numbers please.