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SubjectRe: [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@suse.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@suse.cz>
SUSE Labs, CR


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