Date: Mon, 19 Nov 2012 12:53:25 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Tang Chen <tangchen@cn.fujitsu.com>
Cc: wency@cn.fujitsu.com, linfeng@cn.fujitsu.com, rob@landley.net,
        isimatu.yasuaki@jp.fujitsu.com, laijs@cn.fujitsu.com,
        jiang.liu@huawei.com, kosaki.motohiro@jp.fujitsu.com,
        minchan.kim@gmail.com, mgorman@suse.de, rientjes@google.com,
        yinghai@kernel.org, rusty@rustcorp.com.au,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-doc@vger.kernel.org
Subject: Re: [PATCH 0/5] Add movablecore_map boot option.
Message-Id: <20121119125325.ed1abba0.akpm@linux-foundation.org>
In-Reply-To: <1353335246-9127-1-git-send-email-tangchen@cn.fujitsu.com>
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On Mon, 19 Nov 2012 22:27:21 +0800
Tang Chen <tangchen@cn.fujitsu.com> wrote:

> This patchset provide a boot option for user to specify ZONE_MOVABLE memory
> map for each node in the system.
> 
> movablecore_map=nn[KMG]@ss[KMG]
> 
> This option make sure memory range from ss to ss+nn is movable memory.
> 1) If the range is involved in a single node, then from ss to the end of
>    the node will be ZONE_MOVABLE.
> 2) If the range covers two or more nodes, then from ss to the end of
>    the node will be ZONE_MOVABLE, and all the other nodes will only
>    have ZONE_MOVABLE.
> 3) If no range is in the node, then the node will have no ZONE_MOVABLE
>    unless kernelcore or movablecore is specified.
> 4) This option could be specified at most MAX_NUMNODES times.
> 5) If kernelcore or movablecore is also specified, movablecore_map will have
>    higher priority to be satisfied.
> 6) This option has no conflict with memmap option.

This doesn't describe the problem which the patchset solves.  I can
kinda see where it's coming from, but it would be nice to have it all
spelled out, please.

- What is wrong with the kernel as it stands?
- What are the possible ways of solving this?
- Describe the chosen way, explain why it is superior to alternatives

The amount of manual system configuration in this proposal looks quite
high.  Adding kernel boot parameters really is a last resort.  Why was
it unavoidable here?
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