linux-kernel - Re: [RFC v2] percpu: Add a separate function to merge free areas

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Message-ID: <20141204211912.GG4080@htj.dyndns.org>
Date:	Thu, 4 Dec 2014 16:19:12 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	Leonard Crestez <lcrestez@...acom.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Sorin Dumitru <sdumitru@...acom.com>
Subject: Re: [RFC v2] percpu: Add a separate function to merge free areas

On Thu, Dec 04, 2014 at 03:15:27PM -0600, Christoph Lameter wrote:
> On Thu, 4 Dec 2014, Al Viro wrote:
> 
> > ... except that somebody has not known that and took refcounts on e.g.
> > vfsmounts into percpu.  With massive amounts of hilarity once docker folks
> > started to test the workloads that created/destroyed those in large amounts.
> 
> Well, vfsmounts being a performance issue is a bit weird and unexpected.

Docker usage is pretty wide-spread now, making what used to be
siberia-cold paths hot enough to cause actual scalability issues.
Besides, we're now using percpu_ref for things like aio and cgroup
control structures which can be created and destroyed quite
frequently.  I don't think we can say these are "weird" use cases
anymore.

Thanks.

-- 
tejun
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