linux-kernel - Re: [Bug fix PATCH 2/2] acpi, movablemem_map: Make whatever nodes the kernel resides in un-hotpluggable.

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Date:	Sat, 23 Feb 2013 13:26:36 -0600
From:	Rob Landley <rob@...dley.net>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, jiang.liu@...wei.com,
	wujianguo@...wei.com, hpa@...or.com, wency@...fujitsu.com,
	laijs@...fujitsu.com, linfeng@...fujitsu.com, yinghai@...nel.org,
	isimatu.yasuaki@...fujitsu.com, kosaki.motohiro@...fujitsu.com,
	minchan.kim@...il.com, mgorman@...e.de, rientjes@...gle.com,
	guz.fnst@...fujitsu.com, rusty@...tcorp.com.au, lliubbo@...il.com,
	jaegeuk.hanse@...il.com, tony.luck@...el.com,
	glommer@...allels.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [Bug fix PATCH 2/2] acpi, movablemem_map: Make whatever nodes
 the kernel resides in un-hotpluggable.

On 02/20/2013 05:00:56 AM, Tang Chen wrote:
> There could be several memory ranges in the node in which the kernel  
> resides.
> When using movablemem_map=acpi, we may skip one range that have  
> memory reserved
> by memblock. But if it is too small, then the kernel will fail to  
> boot. So, make
> the whole node which the kernel resides in un-hotpluggable. Then the  
> kernel has
> enough memory to use.
> 
> Reported-by: H Peter Anvin <hpa@...or.com>
> Signed-off-by: Tang Chen <tangchen@...fujitsu.com>

Docs part Acked-by: Rob Landley <rob@...dley.net> (with minor  
non-blocking snark).

> @@ -1673,6 +1675,10 @@ bytes respectively. Such letter suffixes can  
> also be entirely omitted.
>  			satisfied. So the administrator should be  
> careful that
>  			the amount of movablemem_map areas are not too  
> large.
>  			Otherwise kernel won't have enough memory to  
> start.
> +			NOTE: We don't stop users specifying the node  
> the
> +			      kernel resides in as hotpluggable so that  
> this
> +			      option can be used as a workaround of  
> firmware
> +                              bugs.

I usually see workaround "for", not "of". And your whitespace is  
inconsistent on that last line.

And I'm now kind of curious what such a workaround would accomplish,  
but I'm suspect it's obvious to people who wind up needing it.

>  	MTD_Partition=	[MTD]
>  			Format: <name>,<region-number>,<size>,<offset>
> diff --git a/arch/x86/mm/srat.c b/arch/x86/mm/srat.c
> index b8028b2..79836d0 100644
> --- a/arch/x86/mm/srat.c
> +++ b/arch/x86/mm/srat.c
> @@ -166,6 +166,9 @@ handle_movablemem(int node, u64 start, u64 end,  
> u32 hotpluggable)
>  	 * for other purposes, such as for kernel image. We cannot  
> prevent
>  	 * kernel from using these memory, so we need to exclude these  
> memory
>  	 * even if it is hotpluggable.
> +	 * Furthermore, to ensure the kernel has enough memory to boot,  
> we make
> +	 * all the memory on the node which the kernel resides in
> +	 * un-hotpluggable.
>  	 */

Can you hot-unplug half a node? (Do you have a choice with the  
granularity here?)

Rob
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