linux-kernel - Re: [PATCH] Driver Core: devtmpfs - kernel-maintained tmpfs-based /dev

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Date:	Sat, 8 Aug 2009 10:11:24 -0700
From:	Greg KH <greg@...ah.com>
To:	Al Boldi <a1426z@...ab.com>
Cc:	Chris Friesen <cfriesen@...tel.com>,
	Andi Kleen <andi@...stfloor.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, Kay Sievers <kay.sievers@...y.org>,
	Jan Blunck <jblunck@...e.de>, gregkh@...e.de,
	Harald Hoyer <harald@...hat.com>,
	Scott James Remnant <scott@...ntu.com>
Subject: Re: [PATCH] Driver Core: devtmpfs - kernel-maintained tmpfs-based
 /dev

On Sat, Aug 08, 2009 at 12:14:39PM +0300, Al Boldi wrote:
> Greg KH wrote:
> > On Sat, Aug 08, 2009 at 12:17:31AM +0300, Al Boldi wrote:
> > > For devtmpfs to be a realistic replacement for static /dev, it has to
> > > be comparable to static /dev in both speed and size.
> >
> > Since when is this requirement necessary?  You want something for free
> > in both speed and size?  Well, you got it in speed, but not size, it
> > will take up memory that is swapable, and a tiny ammount of non-swapable
> > kernel memory for the code.
> 
> Not so tiny when you count in the hotplug dependency.

devtmpfs does not rely on hotplug at all.

> > > WRT speed, there should be no  slowdown and it should be just as fast
> > > as a "tar -xp < dev.tar".
> >
> > Again, where is this requirement coming from?
> >
> > Have you timed devtmpfs?
> 
> Not yet, I am still waiting for the latest patch against .30.

I already pointed you at it.

> > > WRT size, it should not be dependent on hotplug, and instead offer
> > > hotplug as an option.
> >
> > Um, again, who made up such a requirement?  Are you running systems
> > today with CONFIG_HOTPLUG disabled?  If so, how well is that working for
> > you?
> 
> It's working out quite well.  I don't like hotplug, it's too slow.  I always 
> turn it and module-autoloading off, to achieve a much more responsive system.

What becomes "more responsive"?  What is too slow?

Anyway, this is quite off-topic for the original patch.  If you have
problems/issues with udev and CONFIG_HOTPLUG, let's take that to the
linux-hotplug@...r.kernel.org list.

thanks,

greg k-h
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