linux-kernel - Re: [patch 11/33] fs: dcache scale subdirs

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Message-ID: <1277277795.1875.748.camel@laptop>
Date:	Wed, 23 Jun 2010 09:23:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	john stultz <johnstul@...ibm.com>
Cc:	Nick Piggin <npiggin@...e.de>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, John Kacur <jkacur@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 11/33] fs: dcache scale subdirs

On Tue, 2010-06-22 at 19:03 -0700, john stultz wrote:

> > Well, you make lockdep very unhappy by locking multiple dentries
> > (unbounded number) all in the same lock class.
> 
> So.. Is there a way to tell lockdep that the nesting is ok (I thought
> that was what the spin_lock_nested call was doing...)? 

spin_lock_nested() allows you to nest a limited number of locks (up to
8, although the usual case is 1).

> Or is locking a (possibly quite long) chain of objects really just a
> do-not-do type of operation? 

Usually, yeah. It would be really nice to do this another way (also for
scalability, keeping a large subtree locked is bound to to lead to more
contention).
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