linux-kernel - Re: [PATCH 1/3] mem-hotplug: introduce movablenode option

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Message-Id: <20160811161335.8599521d14927394f1208fc7@linux-foundation.org>
Date:	Thu, 11 Aug 2016 16:13:35 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Xishi Qiu <qiuxishi@...wei.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Vlastimil Babka <vbabka@...e.cz>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Michal Hocko <mhocko@...e.com>,
	David Rientjes <rientjes@...gle.com>,
	"Joonsoo Kim" <iamjoonsoo.kim@....com>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	"'Kirill A . Shutemov'" <kirill.shutemov@...ux.intel.com>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] mem-hotplug: introduce movablenode option

On Thu, 4 Aug 2016 19:23:54 +0800 Xishi Qiu <qiuxishi@...wei.com> wrote:

> This patch introduces a new boot option movablenode.
> 
> To support memory hotplug, boot option "movable_node" is needed. And to
> support debug memory hotplug, boot option "movable_node" and "movablenode"
> are both needed.
> 
> e.g. movable_node movablenode=1,2,4

I have some naming concerns.  "movable_node" and "movablenode" is just
confusing and ugly.

Can we just use the one parameter?   eg,

	vmlinux movable_node

or

	vmlinux movable_node=1,2,4

if not that, then how about "movable_node" and "movable_nodes"?  Then
every instance of "movablenode" in the patch itself should become
"movable_nodes" to be consistent with the command line parameter.

> It means node 1,2,4 will be set to movable nodes, the other nodes are
> unmovable nodes. Usually movable nodes are parsed from SRAT table which
> offered by BIOS, so this boot option is used for debug.
> 
>
> ---
>  Documentation/kernel-parameters.txt |  4 ++++
>  arch/x86/mm/srat.c                  | 36 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 40 insertions(+)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 82b42c9..f8726f8 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2319,6 +2319,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  	movable_node	[KNL,X86] Boot-time switch to enable the effects
>  			of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
>  
> +	movablenode=	[KNL,X86] Boot-time switch to set which node is
> +			movable node.
> +			Format: <movable nid>,...,<movable nid>

I think the docs should emphasize that this option disables the usual
SRAT-driven allocation and replaces it with manual allocation.

Also, can we please have more details in the patch changelog?  Why do we
*need* this?  Just for debugging?  Normally people will just use
SRAT-based allocation so normal users won't use this?  If so, why is
this debugging feature considered useful enough to add to the kernel?