linux-kernel - Re: [PATCH] memory hotplug disable boot option

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Date:	Thu, 1 Jul 2010 12:30:57 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Nathan Fontenot <nfont@...tin.ibm.com>
Cc:	Greg KH <gregkh@...e.de>, Dave Hansen <dave@...ux.vnet.ibm.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH] memory hotplug disable boot option

On Wed, 30 Jun 2010 22:17:35 -0500
Nathan Fontenot <nfont@...tin.ibm.com> wrote:

> On 06/30/2010 07:31 PM, KAMEZAWA Hiroyuki wrote:
> > On Wed, 30 Jun 2010 08:47:55 -0700
> > Greg KH <gregkh@...e.de> wrote:
> >>> and adding a scalable interface for large scale machines ?
> >>> I'd like to consider something..
> >>
> >> Dynamically changing the layout on big memory boxes makes sense to me,
> >> how about you?
> >>
> > 
> > like this ?
> > ==
> > boot option:
> > memory_sysfs_layout=compact
> > memory_sysfs_layout=auto (default)
> > memory_sysfs_layout=full
> > 
> > Considering briefly, how about this compact layout ?
> > 
> > /sys/devices/system/memory/:
> >                             list, hide, show, memoryX...
> > 
> > list: // show available memory index list.
> >   #cat list
> >    0 1 2 ....10000...
> > 
> > show: //an interface to enable the interface.
> >   #echo INDEX > memory_index
> >   will create memoryINDEX diretory.
> > 
> > hide: //an interface to hide the interface.
> >   #echo INDEX > memory_hide
> >   will remove memoryINDEX sysfs directory.
> > 
> > 
> > In compact mode, all memoryX interface are hidden at boot.
> > In full mode, all memoryX interaface are shown.
> > The Boot option just affects status at boot. If users want, he can make
> > all memory sysfs in shown state.
> 
> Do we need to make something as complicated as dynamically adding and removing
> the sysfs directories?  Why not a compact layout that just takes the files
> that currently reside in the memoryXX dirs and move them up to the memory
> directory. This would be state (which should probably be split into an
> 'online' and 'offline' file), removable, phys_index, and phys_device.
> 
I've considered several patterns.

with 4096 bytes buffer of sysfs, "printting bitmap" just covers small
amount of sections even with smart ASCII format to show contiguous range
as a chunk. That's my concern. (and 'list' file in above example
is impossible to impelement.)

If I can use rmdir/mkdir interface, it's much simple rather than above "echo".
But it seems impossible.
Because we have memory information in /proc/iomem already, I think hide/show
interface (instead of mkdir/rmdir) is not very bad.

If you can implement highly scalable interface, please.
I just stop dreaming and ack yours.

Thanks,
-Kame


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