Re: [PATCH v5 6/6] mem-hotplug: Introduce movablenode boot option

[Tejun Heo <tj@kernel.org>]

On Wed, Sep 25, 2013 at 02:35:14AM +0800, Zhang Yanfei wrote:
> From: Tang Chen <tangchen@cn.fujitsu.com>
> 
> The hot-Pluggable field in SRAT specifies which memory is hotpluggable.
> As we mentioned before, if hotpluggable memory is used by the kernel,
> it cannot be hot-removed. So memory hotplug users may want to set all
> hotpluggable memory in ZONE_MOVABLE so that the kernel won't use it.
> 
> Memory hotplug users may also set a node as movable node, which has
> ZONE_MOVABLE only, so that the whole node can be hot-removed.
> 
> But the kernel cannot use memory in ZONE_MOVABLE. By doing this, the
> kernel cannot use memory in movable nodes. This will cause NUMA
> performance down. And other users may be unhappy.
> 
> So we need a way to allow users to enable and disable this functionality.
> In this patch, we introduce movablenode boot option to allow users to
> choose to not to consume hotpluggable memory at early boot time and
> later we can set it as ZONE_MOVABLE.
> 
> To achieve this, the movablenode boot option will control the memblock
> allocation direction. That said, after memblock is ready, before SRAT is
> parsed, we should allocate memory near the kernel image as we explained
> in the previous patches. So if movablenode boot option is set, the kernel
> does the following:
> 
> 1. After memblock is ready, make memblock allocate memory bottom up.
> 2. After SRAT is parsed, make memblock behave as default, allocate memory
>    top down.
> 
> Users can specify "movablenode" in kernel commandline to enable this
> functionality. For those who don't use memory hotplug or who don't want
> to lose their NUMA performance, just don't specify anything. The kernel
> will work as before.
> 
> Suggested-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
> Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>

I hope the param description and comment were better.  Not necessarily
longer, but clearer, so it'd be great if you can polish them a bit
more.  Other than that,

 Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun

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