linux-kernel - Re: [PATCH] drivers: base: new memory config sysfs driver for large memory systems

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Message-ID: <20130726143344.GA4379@variantweb.net>
Date:	Fri, 26 Jul 2013 09:33:44 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Nathan Fontenot <nfont@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Nivedita Singhvi <niv@...ibm.com>,
	Michael J Wolf <mjwolf@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers: base: new memory config sysfs driver for large
 memory systems

On Thu, Jul 25, 2013 at 04:38:00PM -0700, Greg Kroah-Hartman wrote:
> On Thu, Jul 25, 2013 at 04:11:20PM -0500, Seth Jennings wrote:
> > From: Nathan Fontenot <nfont@...ux.vnet.ibm.com>
> > 
> > Large memory systems (1TB or more) experience boot delays on the order
> > of minutes due to the initializing the memory configuration part of
> > sysfs at /sys/devices/system/memory/.
> > 
> > ppc64 has a memory block size of 256M and (I think) x86 is 128M.  With 1TB
> > of RAM and a 256M block size, that's 4k memory blocks with 20 sysfs
> > entries per block that's around 80k items that need be created at boot
> > time in sysfs.  Some systems go up to 16TB where the issue is
> > even more severe.
> > 
> > This patch is a prototype for a new sysfs memory layout where the
> > entries are created on demand by writing memory block numbers into a
> > "show" and "hide" files to create and destroy the memory block
> > configuration attributes in sysfs.  This would decouple the number of
> > sysfs entries created at boot time from the memory size, resulting in a
> > sysfs initialization time that doesn't increase and memory size
> > increase.
> > 
> > Signed-off-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>
> > Signed-off-by: Nathan Fontenot <nfont@...ux.vnet.ibm.com>
> 
> How does this tie into the patches Nathan sent yesterday for memory
> hotplug stuff that I thought modified the same part of the kernel?

So this patch introduces the new layout in a new file
drives/base/memfs.c (which, in light of your last comment should
probably be something more like largememory.c).

It doesn't clash with Nathan's, but it doesn't contain the new
is_memblock_[removable|offline] functions or the new "release"
attribute.  But that can be added easily.

Seth

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