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

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Date:   Tue, 3 Jul 2018 18:35:32 +0000
From:   "Nikunj Kela (nkela)" <nkela@...co.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     Will Deacon <will.deacon@....com>,
        "xe-kernel@...ernal.cisco.com" <xe-kernel@...ernal.cisco.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] arm64: add support for 43bit physical address

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)

Thanks,
-Nikunj
________________________________________
From: Catalin Marinas <catalin.marinas@....com>
Sent: Tuesday, July 3, 2018 7:56 AM
To: Nikunj Kela (nkela)
Cc: Will Deacon; xe-kernel@...ernal.cisco.com; linux-kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org
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.

--
Catalin