linux-kernel - Re: [RESEND][PATCH] Add /proc/mempool to display mempool usage

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Date:	Mon, 01 Dec 2008 13:13:31 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Randy Dunlap <randy.dunlap@...cle.com>
Cc:	Greg KH <greg@...ah.com>, Alexey Dobriyan <adobriyan@...il.com>,
	Remi Colinet <remi.colinet@...il.com>,
	linux-kernel@...r.kernel.org, akpm@...l.org, torvalds@...l.org,
	linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RESEND][PATCH] Add /proc/mempool to display mempool usage

On Mon, 2008-12-01 at 10:12 -0800, Randy Dunlap wrote:
> On Sat, 29 Nov 2008 15:49:07 -0800 Greg KH wrote:
> 
> > On Sun, Nov 30, 2008 at 12:42:07AM +0300, Alexey Dobriyan wrote:
> > > On Sat, Nov 29, 2008 at 06:44:49PM +0100, Remi Colinet wrote:
> > > > This patch add a new /proc/mempool file in order to display mempool usage.
> > > > 
> > > > The feature can be disabled with CONFIG_PROC_MEMPOOL=N during kernel
> > > > configuration.
> > > 
> > > We're NOT adding config option per proc file.
> > > 
> > > And can we, please, freeze /proc for not per-process stuff and open debugfs
> > > for random stuff, please?
> > 
> > debugfs has been open for random stuff since the day it was added to the
> > tree :)
> > 
> > Feel free to put this kind of thing there instead of proc.
> 
> Do distros ship with debugfs enabled?
> The problem with using debugfs is that it is very optional IMO.

The problem with debugfs is that it claims to not be an ABI but it is
lying. Distributions ship tools that depend on portions of debugfs. And
they also ship debugfs in their kernel. So it is effectively the same
as /proc, except with the 1.0-era everything-goes attitude rather than
the 2.6-era we-should-really-think-about-this one.

Pushing stuff from procfs to debugfs is thus just setting us up for pain
down the road. Don't do it. In five years, we'll discover we can't turn
debugfs off or even clean it up because too much relies on it.

If you think that debugfs is NOT an ABI, then I'm sure you'll be happy
to ack my patch entitled 'gratuitously break usbmon to remind folks that
debugfs is not an ABI'.

-- 
Mathematics is the supreme nostalgia of our time.

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