linux-ext4 - Re: [PATCH 01/11] quota: Improve locking

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Message-ID: <20090126100427.GA2726@duck.suse.cz>
Date:	Mon, 26 Jan 2009 11:04:27 +0100
From:	Jan Kara <jack@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 01/11] quota: Improve locking

On Fri 23-01-09 23:49:12, Andrew Morton wrote:
> On Fri, 16 Jan 2009 19:08:09 +0100 Jan Kara <jack@...e.cz> wrote:
> 
> >  static DEFINE_SPINLOCK(dq_list_lock);
> > +static DEFINE_SPINLOCK(dq_state_lock);
> >  DEFINE_SPINLOCK(dq_data_lock);
> 
> The chances are very good that two or even three of these locks will
> all get placed into the same cacheline in main memory.  The effects
> will be quite bad if different CPUs (or, worse, different nodes) are
> taking these locks.
>
> For single, kernel-wide locks like these I think we should almost
> always pad out to a cacheline.
  I never thought about this. Thanks for the idea.

> With __cacheline_aligned_in_smp, rather than __cacheline_aligned. 
> Because spinlocks do take space even in uniprocessor builds.
  I've added this to my list of quota cleanups.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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