linux-kernel - Re: [PATCH v3 2/2] mm: Introduce kernelcore=mirror option

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Message-Id: <20151228142108.fa679ebf9d3a91ad14924977@linux-foundation.org>
Date:	Mon, 28 Dec 2015 14:21:08 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Taku Izumi <izumi.taku@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	tony.luck@...el.com, qiuxishi@...wei.com,
	kamezawa.hiroyu@...fujitsu.com, mel@....ul.ie,
	dave.hansen@...el.com, matt@...eblueprint.co.uk
Subject: Re: [PATCH v3 2/2] mm: Introduce kernelcore=mirror option

On Wed,  9 Dec 2015 12:19:37 +0900 Taku Izumi <izumi.taku@...fujitsu.com> wrote:

> This patch extends existing "kernelcore" option and
> introduces kernelcore=mirror option. By specifying
> "mirror" instead of specifying the amount of memory,
> non-mirrored (non-reliable) region will be arranged
> into ZONE_MOVABLE.
> 
> v1 -> v2:
>  - Refine so that the following case also can be
>    handled properly:
> 
>  Node X:  |MMMMMM------MMMMMM--------|
>    (legend) M: mirrored  -: not mirrrored
> 
>  In this case, ZONE_NORMAL and ZONE_MOVABLE are
>  arranged like bellow:
> 
>  Node X:  |MMMMMM------MMMMMM--------|
>           |ooooooxxxxxxooooooxxxxxxxx| ZONE_NORMAL
>                 |ooooooxxxxxxoooooooo| ZONE_MOVABLE
>    (legend) o: present  x: absent
> 
> v2 -> v3:
>  - change the option name from kernelcore=reliable
>    into kernelcore=mirror
>  - documentation fix so that users can understand
>    nn[KMS] and mirror are exclusive

My earlier concern with this approach is the assumption that *all* of
the mirrored memory will be used to kernelcore.  The user might want to
use half the machine's mirrored memory for kernelcore and half for
regular memory but cannot do so.

However I think what I'm seeing from the discussion is that in this
case, the user can alter the amount of mirrored memory via EFI to
achieve the same effect.

Is this correct?  If so, should we document this somewhere and provide
our users with instructions on how to make the required EFI changes? 
Or is this all so totally obvious to them that there is no need?

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