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From: Oliver Neukum <oliver@neukum.org>
Organization: Novell
To: Matthew Wilcox <matthew@wil.cx>
Subject: Re: [PATCH] Replace completions with semaphores
Date: Wed, 16 Apr 2008 18:42:50 +0200
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Cc: Ingo Oeser <ioe-lkml@rameria.de>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andi Kleen <andi@firstfloor.org>, Peter Zijlstra <peterz@infradead.org>,
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       Roland Dreier <rdreier@cisco.com>, Ingo Molnar <mingo@elte.hu>,
       Daniel Walker <dwalker@mvista.com>, linux-kernel@vger.kernel.org
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Am Mittwoch, 16. April 2008 18:34:14 schrieb Matthew Wilcox:
> On Wed, Apr 16, 2008 at 06:31:08PM +0200, Oliver Neukum wrote:
> > Am Mittwoch, 16. April 2008 18:16:52 schrieb Matthew Wilcox:
> > > The basic idea is that you get back a cookie from the kcounter_claim()
> > > which you have to hand to the kcounter_release() function so it
> > > knows which one you released. ?It's similar to mutex debugging except
> > 
> > So in addition to the kcounter we need to save a token in a data structure?
> > In fact, there must be a data structure that can house that token. So you
> > can no longer live with a pointer just to a device descriptor, but every
> > individual use of a resource must have an associated data structure?
> 
> That's right.  Do you have an example where this would be inconvenient?
> I couldn't find one.  For example, with USB, you could place one in the
> struct urb.

That's a data structure we really want to shrink. And furthermore, the needs
of the use cases should shape the locking primitives, not the reverse.

	Regards
		Oliver