linux-kernel - Re: Important for fs devs: rcu-walk merged upstream

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Date:	Wed, 12 Jan 2011 00:06:42 +1100
From:	Nick Piggin <npiggin@...il.com>
To:	Nick Piggin <npiggin@...il.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Important for fs devs: rcu-walk merged upstream

On Tuesday, January 11, 2011, Joel Becker <jlbec@...lplan.org> wrote:
> On Sat, Jan 08, 2011 at 01:54:47PM +1100, Nick Piggin wrote:
>> The rcu-walk stuff can be more tricky for your filesystem
>> to take advantage of.
>>
>> If you supply a .d_revalidate, .permission, or .check_acl,
>> then path walking is going to be slow and unscalable for
>> you.
>
>         Do you mean "as slow and unscalable as it has always been" or
> "even slower now"?  A quick look suggests the former, but I wanted to be
> sure.

Yeah it should be about the same. Bit more complex code so it might be
a bit slower. A few code and branch and cache improvements so it might
be a bit faster. Refcounts on the same dentry become a bit less
scalable for using lock instead of atomic. On the other hand dropping
the ref on leaf denty doesn't require global lock.

It should not be urgent for 2.6.38.
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