linux-kernel - Re: [PATCH 23/32] Generic dynamic per cpu refcounting

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Message-ID: <20130125020943.GH2373@mtj.dyndns.org>
Date:	Thu, 24 Jan 2013 18:09:43 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-aio@...ck.org,
	linux-fsdevel@...r.kernel.org, zab@...hat.com, bcrl@...ck.org,
	jmoyer@...hat.com, axboe@...nel.dk, viro@...iv.linux.org.uk,
	tytso@....edu, Oleg Nesterov <oleg@...hat.com>,
	srivatsa.bhat@...ux.vnet.ibm.com, Christoph Lameter <cl@...ux.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 23/32] Generic dynamic per cpu refcounting

Hello, again.

On Thu, Jan 24, 2013 at 06:03:40PM -0800, Tejun Heo wrote:
> Yeah, if we're aiming to replace refcnts in file and kobj, dynamic
> alloc may be justified.  Hopefully, the accounting necessary to decide
> whethre to use percpu isn't too burdensome.

Ooh, I forgot one thing.  We might not gain much by replacing file
refcnt w/ this.  You can't really get cheaper than fget_light().
Also, while kobj destruction can still be considered an infrequent
operation, file destruction is not and people will get mighty unhappy
if you do synchronize_sched/rcu() from fput() synchronously.

So, I'm now back to "do we need dynamic allocation".  What else do we
have to convert?

Thanks.

-- 
tejun
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