linux-kernel - Re: [PATCH v2 0/2] mm: Introduce kernelcore=reliable option

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Message-Id: <20151207163112.930a495d24ab259cad9020ac@linux-foundation.org>
Date:	Mon, 7 Dec 2015 16:31:12 -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 v2 0/2] mm: Introduce kernelcore=reliable option

On Sat, 28 Nov 2015 00:03:55 +0900 Taku Izumi <izumi.taku@...fujitsu.com> wrote:

> Xeon E7 v3 based systems supports Address Range Mirroring
> and UEFI BIOS complied with UEFI spec 2.5 can notify which
> ranges are reliable (mirrored) via EFI memory map.
> Now Linux kernel utilize its information and allocates
> boot time memory from reliable region.
> 
> My requirement is:
>   - allocate kernel memory from reliable region
>   - allocate user memory from non-reliable region
> 
> In order to meet my requirement, ZONE_MOVABLE is useful.
> By arranging non-reliable range into ZONE_MOVABLE,
> reliable memory is only used for kernel allocations.
> 
> My idea is to extend existing "kernelcore" option and
> introduces kernelcore=reliable option. By specifying
> "reliable" instead of specifying the amount of memory,
> non-reliable region will be arranged into ZONE_MOVABLE.

It is unfortunate that the kernel presently refers to this memory as
"mirrored", but this patchset introduces the new term "reliable".  I
think it would be better if we use "mirrored" throughout.

Of course, mirroring isn't the only way to get reliable memory. 
Perhaps if a part of the system memory has ECC correction then this
also can be accessed using "reliable", in which case your proposed
naming makes sense.  reliable == mirrored || ecc?

Secondly, does this patchset mean that kernelcore=reliable and
kernelcore=100M are exclusive?  Or can the user specify
"kernelcore=reliable,kernelcore=100M" to use 100M of reliable memory
for kernelcore?

This is unclear from the documentation and I suggest that this be
spelled out.

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