Re: [patch 0/3] Turn CONFIG_HOTPLUG always on.

From: Greg KH <gregkh@linuxfoundation.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
	Ralf Baechle <ralf@linux-mips.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Chris Metcalf <cmetcalf@tilera.com>,
	Chris Zankel <chris@zankel.net>,
	linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
	Tim Bird <tim.bird@am.sony.com>
Subject: Re: [patch 0/3] Turn CONFIG_HOTPLUG always on.
Date: Fri, 5 Oct 2012 07:32:46 -0700	[thread overview]
Message-ID: <20121005143246.GA18276@kroah.com> (raw)
In-Reply-To: <20121005015036.0d0b7ebd.akpm@linux-foundation.org>

On Fri, Oct 05, 2012 at 01:50:36AM -0700, Andrew Morton wrote:
> On Thu, 6 Sep 2012 13:28:16 -0700 Greg KH <gregkh@linuxfoundation.org> wrote:
> 
> > On Tue, Sep 04, 2012 at 05:01:05PM -0700, Greg Kroah-Hartman wrote:
> > > From: Greg KH <gregkh@linuxfoundation.org>
> > > 
> > > The CONFIG_HOTPLUG variable is tough to turn off, and almost all arches
> > > default to it on.
> > > 
> > > If you turn it off, it saves you a big 200 or so bytes, and then starts
> > > to cause all sorts of problems as the code paths if the option is
> > > disabled is never really tested, and memory segments start to get thrown
> > > away that driver authors assume will always be present.
> > > 
> > > So, as part of trying to get rid of the option entirely, let's just turn
> > > the option always on.
> > > 
> > > Note, to do this properly, I found two duplicate definitions of the
> > > option, in the Tile and Xtensa arch files, this patch series removes
> > > those duplicates first.
> > > 
> > > Anyone object to me just taking these three patches through my
> > > driver-core tree for 3.7?  After this set, I'll start unwinding the
> > > places where CONFIG_HOTPLUG is used and remove the parts that are not
> > > used anymore now that the option can not be turned off.
> > 
> > Given the lack of objection, I've now queued these up for 3.7 and will
> > start unwinding the CONFIG_HOTPLUG mess.
> > 
> 
> I wonder if this has had sufficient consideration.
> 
> It isn't just 200 bytes, is it?  It's all memory which is marked
> __devinit* and __devexit* - that's a tremendous amount of stuff.  We
> should quantify it.
> 
> It wouldn't surprise me if there are organizations who are using
> CONFIG_HOTPLUG=n effectively.  We regularly bust a gut to save a few
> bytes and for people who really care about this we're here sending them
> backwards a lot further than that.

Given the recent round of patches that I've applied to the tree making
it so that CONFIG_HOTPLUG=n actually boots and works, that were needed
for the past 6+ kernel versions, I find it very unlikely anyone actually
runs a system in this type of configuration, but I would love to hear
from someone who does if they are out there.

greg k-h