Re: [PATCH v10 04/35] dentry: move to per-sb LRU locks

Dave Chinner
2013-06-06T01:56:50Z

On Wed, Jun 05, 2013 at 04:07:38PM -0700, Andrew Morton wrote:
> On Mon, 3 Jun 2013 23:29:33 +0400 Glauber Costa <glommer@openvz.org> wrote:
>
> > From: Dave Chinner <dchinner@redhat.com>
> >
> > With the dentry LRUs being per-sb structures, there is no real need
> > for a global dentry_lru_lock. The locking can be made more
> > fine-grained by moving to a per-sb LRU lock, isolating the LRU
> > operations of different filesytsems completely from each other.
>
> What's the point to this patch? Is it to enable some additional
> development, or is it a standalone performance tweak?

It's the separation of the global lock into locks of the same scope
the generic LRU list requires.

> If the latter then the patch obviously makes this dentry code bloatier
> and straight-line slower. So we're assuming that the multiprocessor
> contention-avoidance benefits will outweigh that cost. Got any proof
> of this?

Well, it will do that too for workloads that span multiple
filesytems, but that isn't the point of the patch. it's merely a
setting stone...

Cheers,

Dave.

--
Dave Chinner
david@fromorbit.com

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