linux-kernel - Re: 2.6.19-rc5-mm1 progression

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Date:	Wed, 06 Dec 2006 13:12:50 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Larry Finger <Larry.Finger@...inger.net>
Cc:	Andrew Morton <akpm@...l.org>,
	Benoit Boissinot <bboissin@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: 2.6.19-rc5-mm1 progression

On Mon, 2006-12-04 at 21:32 -0600, Larry Finger wrote:
> Andrew Morton wrote:
> > On Fri, 24 Nov 2006 17:36:27 +0100
> > "Benoit Boissinot" <bboissin@...il.com> wrote:
> > 
> >> On 11/24/06, Larry Finger <Larry.Finger@...inger.net> wrote:
> >>> Is there the equivalent of 'git bisect' for the -mmX kernels?
> >>>
> >> http://www.zip.com.au/~akpm/linux/patches/stuff/bisecting-mm-trees.txt
> >>
> > 
> > Please take the time to do that.  Yours is an interesting report - I'm not
> > aware of anything in there which was expected to cause a change of this
> > mature.
> > 
> 
> There are at least two patches in 2.6.19-rc5-mm2 that make my system much more responsive for 
> interactive jobs. The one that has the majority of the effect is:
> 
> radix-tree-rcu-lockless-readside.patch
> 
> I have not been able to isolate the second patch, which has the lesser effect. All I can say is that 
> it occurred before the above patch in patches/series. This patch was tested against 2.6.19 and fixed 
> most of the problem on that version.

Curious...

This patch introduces the direct pointer optimisation for single element
radix trees and makes the radix tree safe to read in a lock-less manner
which is not used -yet-. The only difference that that should have is
that the elements are freed using rcu callback instead of directly.

/me puzzled how this has a large effect on interactivity.

Nick?

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