Re: [PATCH part1 v6 update 6/6] mem-hotplug: Introduce movable_node boot option

[Toshi Kani <toshi.kani@hp.com>]

On Sun, 2013-10-06 at 14:43 +0000, 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 movable_node 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 movable_node 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 movable_node 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 "movable_node" 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>
> Acked-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Tang Chen <tangchen@cn.fujitsu.com>
> Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>

Thanks for the quick update.

Acked-by: Toshi Kani <toshi.kani@hp.com>

-Toshi

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